Where the third stage of Super Saiyan's purpose was 100% utilization of physical stamina, the purpose of the Super Saiyan 3 transformation is to increase the utilization of ki, and as a result, the transformation rapidly consumes the energy of the user. This notably leads to extended levels of fatigue, even long after powering down. If the user has died and is not encumbered by a living body, this strain is reduced somewhat, and additional energy depletion is minimized (such as in Goku's case during his first fight with Majin Buu). The difference between Super Saiyan 3 and Super Saiyan 2, its predecessor, is immediately noticeable as speed, strength and endurance are all pushed far beyond the normal limits. The first time that Goku used this form on Earth, its power caused massive tidal waves and hurricanes and nearly shook the planet apart. During subsequent transformations, Goku seemingly controlled it enough to prevent such dangerous side-effects. In addition, this power could be sensed even as far as the distance between Earth and Supreme Kai's planet, something that not only shocked Supreme Kai, Kibito, and Gohan, but worried them as well.
However, with the enormous power, there are some very serious setbacks stemming from the rapid use of ki energy. When the then-deceased Goku showed Babidi and Majin Buu the form, he cut his remaining temporal revival energy in half, and in the anime when he shows his power to the excitedTrunks and Goten, his energy was completely dissipated, forcing him to return to Other World. Likewise, when the now fully living Super Saiyan 3 Goku attempted to regain energy while Vegeta and Mr. Satan distracted Kid Buu, he was unable to do so, draining his power completely and leaving him in a weakened, normal state where he could not even control the Spirit Bomb. Goku acknowledged that he had little experience with the transformation, with his fight with Kid Buu being the first time he used it in a full fight with a living body. Performing it twice in a short time brought him to his knees and expended all of his remaining energy. (In the manga, he does not revert to his original form until after Vegeta intervenes to buy him the minute that he needed, however.) The fused Gotenks was not able to maintain the transformation for very long either, reverting to his base form after substantially less than thirty minutes transformed.
The energy drain issues are exacerbated even further when Goku is turned back into a child in Dragon Ball GT, where he can only hold the transformation for a couple of seconds and struggles to utilize the power against Baby Vegeta. This limit was lifted somewhat after Goku's tail was restored with the help of Elder Kai, allowing him to sustain the form for a longer duration, though he was still no match for Super Baby Vegeta in this state.
The transformation causes some stark changes in physical appearance. The trademark characteristic of the transformation is the user's hair: the rigid hair of the Super Saiyan 2 state becomes flowing and smooth again, and grows down to or sometimes passes the user's waist. The eyebrows vanish completely, making the forehead and eye ridges appear larger and revealing a more prominent brow ridge. A small increase in muscle mass is evident, and muscle tone is sharply defined. Energy radiation is so great that the aura pulses at an extremely high frequency, almost to the point where it seems static; the sound of the aura is also pitched even higher than that of Super Saiyan 2. Bio-electricity, like in the Super Saiyan 2 form, is again constant, and may reach further outward from the body than before. The Saiyan's voice may become slightly deeper, though this is obviously a feature only found in the anime. If the user of the Super Saiyan 3 form has a tail, it turns yellowish gold. There is no personality change, as no emotion is required to initiate the transformation (Goku acted stoic to intimidate Babidi and Majin Buu, and Gotenks acted as he normally would). Another notable change is that the user seems to "glow" while in this state, more so than before, where the skin and clothes color were lightened, but not as much as the color change of this form (this mostly applies to training gi; when Goku transforms into Super Saiyan 3, his training gi appears to be rather Gold and blue instead of orange and blue).
The Super Saiyan 3 form gives the user four times the strength of a Super Saiyan 2, so it multiplies the Saiyan's base power by 400x times its normal amount. Goku uses the Super Saiyan 3 transformation in a brief battle against Majin Buu in order to stall him long enough for Trunks to find the Dragon Radar. He was able to overtake the monster, completely outmatching him blow for blow. He eventually retreated from the fight, as he wanted Goten and Trunks to defeat Buu with their fusion technique, as he "wouldn't be around forever." Goku later stated he believed he could have killed Buu if he had actually tried, but held complete faith in Gotenks' ability to destroy him if they were to try the Fusion Dance. This form was next seen used by Gotenks, the fusion between Goten and Trunks, during his fight with the new, more powerful version of Majin Buu. While in the Hyperbolic Time Chamber, Piccolo destroyed the only entrance in or out of the dimension, in hopes of trapping Super Buu inside, when he believed that Gotenks had lost and that the universe would be destroyed. Unfortunately, Super Buu was able to escape by ripping the dimensions open using intense sound waves from his own voice when he became angry at the thought of not having anymore food to eat. Learning from the things that Goku taught him about being Super Saiyan 3, Gotenks transforms into Super Saiyan 3 and rips up a hole in a similar fashion, shocking Piccolo. Once outside, Gotenks battled Super Buu in earnest. The two appeared to be an even match, with Gotenks appearing to gain the upper hand before the transformation wore off. The Super Saiyan 3 state was truly pushed to the breaking point in the final battle against Kid Buu. Despite using his full power as a Super Saiyan 3, Goku had difficulty competing with the seemingly endless power supply of the Majin. Though he appeared to have the advantage for most of the fight before the ki drain became evident, his attacks seemed to be useless against Buu, and the transformation eventually caused his collapse from exhaustion. He later revealed that he might have been able to destroy Kid Buu when at full power, but let the fight drag on to give Vegeta a shot. Vegeta then powered up to a Super Saiyan 2 in order to buy him the time that Goku needed to get back up to full strength, but the immense stress of trying to gather his power forced him to revert to his normal state before reaching his maximum potential, leaving him heavily drained and unable to transform. It took a Super Spirit Bomb gathered from all the energies of Earth, the Ogres in Yemma's office, and the Namekian villagers that resided with Moori on New Namek, to finish off Kid Buu, and the Super Saiyan 3 form is never seen in the main manga storyline again. In Dragon Ball GT, Goku's child form caused him to have trouble using Super Saiyan 3. His small body could not handle the energy output of the transformation, and he could only hold it for one minute. When he attempted to fight Baby Vegeta, he was easily beaten down. After having his tail restored, he becomes able to freely use the transformation, but the gap between Baby Vegeta's Super form achieved after receiving all the energies of the half-Saiyans and the Earthlings that he possessed was far too big for him to even land any damage, and he reverted to his normal state, only to transform into a Golden Great Ape, and then into Super Saiyan 4, defeating Baby after a prolonged fight. It was after this fight that Goku discontinued the usage of Super Saiyan 3, as it was heavily outclassed by the raw power and minimal setbacks of Super Saiyan 4.
In Dragon Ball GT, while possessed by Baby, Vegeta transformed into a form where his hair lengthened, he had a single prominent bang that curved across his face and lost his eyebrows: all of those traits of the Super Saiyan 3 form. This had caused some fans to theorize that the additional power that Baby drew from his followers may have caused Vegeta to reach a mutated version of the state, though this was never proven nor stated.
In DragonBall Zeron, this form is used for the first time by Vegeta, Future Trunks and Goku. Vegeta unlocked the transformation through high gravity training and time. Future Trunks did the same, and also unlocked the form. Vegeta is the first one to ever use this form in DragonBall Zeron. Vegeta uses this form to fight Dragon Cooler, Meta Cooler(s) and Dragon Cooler in his final form. Vegeta however, did not win the match, and eventually broke his arm, and had a disadvantage. This form is used more often in the Zets Tournament saga, where Goku and Future Trunks both use this form to face each other in the tournament, and Goku wins. Goku is te strongest Super Saiyan 3 in the series, as he uses his Dragon power and abilities to a far extent. Goku uses this form to face Mystic Gohan, but did not have the upper hand against Mystic Gohan. Though Goku's Super Saiyan 3 powers seem to exceed anyone else's, he still is not as strong as Mystic Gohan is in the form. Future Trunks later uses this form to fight Yougirou in his second form, but loses due to Yougirou's new ice powers. Broly also uses the form to create multiple portals, and also to fight in various battles.
In the movie Dragon Ball Z: Fusion Reborn, Goku uses the Super Saiyan 3 transformation to defeat Janemba, only to have his foe transform into an even more powerful state, "Super" Janemba. Despite holding his own for a good while, Goku is eventually defeated when Super Janemba creates a sword from a discarded Ogre club and begins firing energy blades from it, an attack that Goku has no defense against. It takes the combined efforts of Goku and Vegeta, fused into Gogeta, to take down the demon. In the movie Dragon Ball Z: Wrath of the Dragon, Goku battles the evil monsterHirudegarn in his Super Saiyan 3 form. He is able to kill the monster by using his Dragon Fist technique. Goten and Trunks also fused into Super Saiyan 3 Gotenks during the fight with Hirudegarn, and used his Continuous Die Die Missile attack on Hirudegarn's first stage, followed by a ki blast which seemed successful in destroying the monster. However, Hirudegarn was still alive and transformed into his second form and swatted Gotenks into the ground, hitting him so heavily that he defused and reverted back to Goten and Trunks. It is worth noting that Goku's Super Saiyan 3 transformation appeared to have increased in power to the point that Ultimate Gohan appeared to be considerably weaker than him; Hirudegarn had no difficulty whatsoever in overpowering Ultimate Gohan, but Super Saiyan 3 Goku was able to take multiple hits from the monster and continue fighting. This however, could have been due to Goku's superior fighting intellect, and his Dragon Fist technique, which is one of the most powerful techniques he uses.