Once a Saiyan unlocks their fury, they can activate a change in their body that gives them an extreme boost in strength and speed called Super Saiyan. There are multiple levels of the Super Saiyan form, each proving more difficult to unlock and utilize -- but more powerful -- than the last. However, during Dragon Ball Z, one particular form called Super Saiyan Third Grade, or the Super Saiyan 1.5 transformation, was introduced.
The power boost had a serious flaw, however, that quickly made it one of the least utilized versions of the Super Saiyan transformation. But now, a modern transformation from Dragon Ball Super -- the absurdly fast Ultra Instinct Form -- makes the Super Saiyan 1.5 form even more pointless.
WHAT IS SUPER SAIYAN 1.5?
The Super Saiyan 1.5 form was first introduced during the Cell Saga of Dragon Ball Z. After leaving the Hyperbolic Time Chamber, Future Trunks was able to activate the form. However, both Goku and Vegeta were also aware of the transformation and decided against using it. The transformation forces the full physical reserves of the user into the Super Saiyan transformation, removes many of the natural blocks that would keep someone from utilizing their full strength or stamina all at once.
Unlocking this form augments the muscles and enhances the ki level of the Super Saiyan in question, even increasing the natural size of the user. However, there's a notable weakness to the form -- the increased size and weight of the muscles severely reduces the speed and agility of the user. This, in essence, negates any speed boost that comes from becoming a Super Saiyan, making it near-impossible to fight enemies of similar power levels who have similar top speeds.
Future Trunks's fight with Perfect Cell demonstrates this flaw. While his Super Saiyan 1.5 form might technically be stronger than Cell, it also proves incapable of keeping up with the artificial organism. Cell even mocks Trunks for thinking the power-up would make any real difference. In Dragon Ball Super, Future Trunks best utilizes the form either as a feint (allowing an opponent to underestimate his ability to revert to the speedier Super Saiyan 2 form) or as part of his transformation into his Super Saiyan Rage form. Caulifla eventually develops the transformation during the Tournament of Power story arc, but is quickly and easily dispatched by the superior power of Goku's other transformations -- such as Ultra Instinct.
HOW ULTRA INSTINCT PROVES THIS FORM IS USELESS
Ultra Instinct is (currently) Goku's most powerful form, a state of tranquility that comes out of desperation that enhances Goku's power and speed to immeasurable heights. It transcends anything in the regular Super Saiyan transformation cycle, and is considered a move only available to mythical figures like Whis and Beerus. The form removes any necessity to think while in combat, allowing the user to act purely on instinct. This enhances their speed and agility exponentially, essentially giving the user almost a second sense to dodge incoming attacks. With this form, Goku was actually able to keep up with Jiren and even defeat him -- proving just how much more advantageous it is to have speed over strength in the Dragon Ball universe.
With that kind of speed, someone like Whis can easily outpace Goku and Vegeta at the same time, even when they're in Super Saiyan God form. The most powerful technique in the world is only effective if it can actually be landed -- proving why something like the Super Saiyan 1.5 form is pointless. Just because it amplifies the pure strength of the user doesn't mean the fighter will be skilled enough to use it properly.