Dragon Ball Z's Strongest Super Saiyan Form Is Too Powerful And Totally Useless
Much of the plot of "Dragon Ball Z" is driven by Goku and his allies working on attaining power upgrades to help them defeat whomever might be threatening life on Earth at any given time. Moments like when Goku first turns Super Saiyan or when Gohan stops going Super Saiyan and learns how to achieve his more powerful Mystic Gohan transformation are among some of the series' most memorable. Ironically, however, the strongest Super Saiyan form in all of "Dragon Ball Z" is treated more like an afterthought than a major development and becomes useless almost as soon as it's introduced.
Goku first unveils the Super Saiyan 3 form during the Buu Saga. However, while it amplifies his strength to the greatest degree possible in "Dragon Ball Z," it also drains his stamina at such a rapid rate that it loses all practicality. Furthermore, the transformation can damage its user's surroundings, imbuing its activation with further risk.
Eventually, Goku's son Goten learns to fuse with Vegeta's son Trunks into Gotenks, and in that form, they, too, learn the Super Saiyan 3 transformation. But just like Goku, Gotenks is unable to sustain the form long enough to properly make use of it. While formidable, Super Saiyan 3's strength comes at too great a cost to justify using in battle.
Super Saiyan 3 is difficult to draw
Apparently, one reason the form isn't prevalent in the "Dragon Ball Z" anime is that the show's animators struggled to draw the Super Saiyan 3 form. As it turns out, it wasn't the extravagant hairstyle that posed a challenge, but rather maintaining Goku's recognizable appearance without his eyebrows — a lack of eyebrows being one of the form's key physical changes.
That said, the way the anime incorporates Super Saiyan 3 is largely similar to its manga source material. The fact that Super Saiyan 3 is used so sparingly in the "Dragon Ball" manga has led some fans to speculate that author Akira Toriyama likewise struggled to draw the form and therefore justified its lack of utility in battle. This idea isn't without precedent; in 2018, Kotaku translated a news report revealing that Toriyama decided the Super Saiyan form would turn its user's hair gold after he got tired of shading in Goku's regular black hairstyle.
So, while Toriyama hasn't shared his thoughts on drawing Super Saiyan 3 specifically, he has been known to alter the story of "Dragon Ball" to ease the notoriously strenuous workload required to produce weekly manga chapters. Super Saiyan 3, therefore, may have fallen victim to such a directive, losing its plot relevance as a result.