Dragon Ball Super continually introduces new forms, with Super Saiyan God, Super Saiyan Blue and Ultra Instinct being among the best known. However, some fans have questioned if mastering older forms like Super Saiyan 3 might increase the Saiyan's overall power.
To answer this broader question, we must ask a few more specific ones. Would mastering an older form increase Goku's total ki control and ability, and would it result in his power increasing? And since later forms multiply his powers to a higher degree, would revisiting older, weaker forms still make a difference?
Mastering the Super Saiyan Form Works
As we saw during the Cell Saga, mastering a form function means learning to control ki until the user can channel it in incredible bursts of power. By making Super Saiyan a base form, Goku and Gohan learned to control their ki to the point where they could match Perfect Cell's strength. This helped prepare Gohan for when he ultimately reached the Super Saiyan 2 form. He needed to learn to control his ki to prepare his body for that enhanced process.
By mastering a form's stability, a Saiyan can increase their maximum potential in that form while also improving the power of later forms. Gohan stopped training after the Cell Saga and thus, even at Super Saiyan 2, he was significantly weaker than he was after spending all that time training with Goku leading up to the Cell Games.
This indicates that sustained training at the Super Saiyan level would make it so the user can control ki better and increase their power in later and stronger forms. It was partly because Goku and Vegeta had mastered the Super Saiyan form that they could both transform into one while also in their Super Saiyan God form, thus reaching Super Saiyan Blue. Could mastery of Super Saiyan 3 lead to a Super Saiyan Blue 3 or even further mastery of the Ultra Instinct form?
Will Mastering Super Saiyan 3 Increase Ki Control?
Here's a little-known fact: the Super Saiyan 3 form is actually just the base Super Saiyan form with more ki forced through it. There are multiple non-linear transformations that Goku has unlocked. In a sense, Goku utilizes Super Saiyan 3 by forcing more ki through his system than he can initially handle, causing him to burn through power and go into hyperdrive.
So if Goku truly masters Super Saiyan 3, it leaves the door open as to what will actually happen. There are two options: Goku would be able to maintain Super Saiyan 3 longer and potentially able to integrate this form with other non-linear forms, such as Super Saiyan God. Another possibility is that Super Saiyan 3 might just become Super Saiyan standard with the power multiplier.
Akira Toriyama has speculated that should Goku totally master Super Saiyan 3, that form's physical features would disappear -- allowing Goku to gain the power, control and appearance of standard Super Saiyan with the power multiplier of Super Saiyan 3. This would allow him to progress back up to Super Saiyan 3's forced power control, creating a cycle where Goku can increase in power over and over again as well as increasing his ki Control.
How, then, might this influence the Saiyans' later forms, as fans have wondered? If they can better control their ki, this extrapolates into the different forms as well, especially since Dragon Ball Super has put a greater value on nonlinear transformations. Ki control is essential to maintaining Super Saiyan Blue and Kaio-Ken -- which, given that increased control, will also increase in power. In fact, it might even make forms like Super Saiyan Blue 3 possible, which would make Goku one of the most powerful entities in existence.