Goku turning Super Saiyan on Namek proved to be the push he needed to finally overpower Frieza, turning the tide in a brutal fight that was heavily pushing in Frieza’s favor. Goku’s transformation on Namek is treated like an appropriately grand event, but it’s also a double edged sword. When all else fails, just rely on Super Saiyan.
To be fair, Super Saiyan was explicitly designed to take over as Goku’s “base” form in battles, a fact that would naturally stretchy to the other Saiyans in Dragon Ball. At the same time, this means that fights past Namek often need to rely on Super Saiyan on principle. Dragon Ball is a series where each enemy is stronger than the last, after all.
10 Versus Frieza
There was simply no way the main characters were going to defeat Frieza without Super Saiyan. Every attempt at fighting back against the tyrant proved futile. Vegeta’s plan to make Frieza transform was nipped in the bud with the revelation that Frieza has four forms; Piccolo wasn’t strong enough to defeat Frieza’s third form; and final form Frieza was just toying with Goku the entire time. If Goku didn’t turn Super Saiyan when Krillin was killed, everyone in the main cast would have died on Namek.
9 Versus Mecha-Frieza & King Cold
Heading into the fight with Mecha-Frieza & King Cold, Gohan and the rest of the Dragon Team sincerely doubt how they’ll be able to defeat Frieza. In the time since Goku supposedly killed Frieza on Namek, no one in the main cast has gotten close to his level. By all accounts, Mecha-Frieza should be stronger too.
Thankfully, Future Trunks arrives as a Super Saiyan just in time to kill Frieza like he’s nothing. In Trunks’ future, Goku uses Instant Transmission to teleport to Frieza and his father before they can fight the main cast, logically relying on Super Saiyan to kill them both.
8 Versus Android 19 & Dr. Gero
Without Vegeta triggering Super Saiyan on his own, the three years of training leading up to the Android attack would have been for nothing. Even if Goku was strong enough to defeat Android 19 and Dr. Gero himself, his Heart Virus would have kept him in check against Androids 16, 17, & 18 (who, specifically designed to kill him, would not have let Goku survive.)
Vegeta showing up as a Super Saiyan saves Goku’s life and gives the Dragon Team an opportunity to find Dr. Gero’s lab. Unfortunately, Vegeta sees this as a chance to fight stronger opponents and lets Gero activate his Androids.
7 Versus Semi-Perfect Cell
Following the Dragon Team’s defeat at the hands of the Androids along with Cell’s arrival, Goku realizes that they have no chance of defeating the Artificial Humans unless they train in the Room of Spirit and Time. Vegeta & Trunks go in first, with both of them developing their own forms of Super Saiyan: Grade 2 and Grade 3, respectively.
Vegeta’s Grade 2 is so strong that he beats Semi-Perfect Cell into completely mental submission. Cell is forced to beg Vegeta to let him absorb Android 18, using the fact the Saiyan wants a better fight to his advantage. In letting Cell absorb 18, however, Vegeta squanders any chance he had of killing him.
6 Versus Cell Juniors
Gohan was always strong enough to defeat Cell during the Cell Games, but he didn’t have the confidence or right mindset. It isn’t until Cell kills Android 16 right before his eyes that push comes to shove and Gohan taps into Super Saiyan 2, giving him the rage he needs to finally defeat Cell on his own terms. As part of his inaugural burst of violence, Super Saiyan 2 Gohan slaughters every single Cell Junior that had been terrorizing the Dragon Team. In a single instance, Gohan changes the entire course of the Cell Games.
5 Versus Perfect Cell
Which he immediately lets get to his head. Instead of killing Cell when he has the chance, Gohan plays with his food. Much like how Goku wanted to humiliate Frieza on Namek, Gohan wants to do the same to Cell. Unfortunately, where Goku was on a dying Namek with no one to worry about, Gohan was fighting on a very much still alive Earth.
Pushed to his breaking point, Cell vows to blow himself up. Goku sacrifices his life, but Cell comes back anyways, severely wounding Gohan in the process. Despite all this, Gohan is still physically strong enough to kill Super Perfect Cell with a one handed Kamehameha (albeit with a pep talk from Goku.)
4 Versus Yakon
Yakon’s species feed off light and fight entirely in darkness, making it difficult for Goku to fight in Super Saiyan without getting his Ki drained. Rather than fighting Yakon head on, Goku realizes a fairly quick way of killing Yakon. By intentionally feeding him his Super Saiyan Ki, Goku lures Yakon into a false sense of security where he quickly taps into Super Saiyan 2, overfeeding him and killing Yakon on the spot.
3 Versus Pure Buu
For as well planned as Vegeta’s gambit during Dragon Ball Z’s final battle is, he doesn’t account for Goku’s lack of stamina until he’s already fired the Genki Dama at Pure Buu. Having already exhausted all his Ki trying to charge up Super Saiyan 3, Goku has to use the Genki Dama in his base form – relying on everyone else’s energy. Because the Dragon Team left one wish untouched on Porunga, however, they’re able to wish Goku’s energy back. With a full burst of Super Saiyan, Goku pushes the Genki Dama into Majin Buu, finally killing him.
2 Versus Golden Frieza
Frieza’s time in Earth’s Hell isn’t particularly pleasant for him, but it does give him time to reflect on his failures in life. When he’s revived at the start of Resurrection F, Frieza is ready for revenge, but not without a game plan: training. In the span of four months, Frieza becomes stronger than even Super Saiyan God Goku from Battle of Gods.
If Goku and Vegeta hadn’t triggered Super Saiyan Blue by training with Whis, they both would have been defeated by Golden Frieza. For all of Frieza’s issues with stamina, there’s enough evidence that his Golden form was actually stronger than Super Saiyan Blue.
1 Versus Goku Black
Vegeta takes an incredibly creative approach to fighting Goku Black in the manga. To mitigate the stamina issues related to Super Saiyan Blue, Vegeta uses Super Saiyan God as his base form during their rematch, only tapping into Super Saiyan Blue when connecting damage into Goku Black.
By tapping into Super Saiyan Blue in such short bursts, Vegeta is able to periodically trigger the form and use the full brunt of its power without any stamina issues plaguing him. Goku Black suffers a humiliating beatdown, saved only by his other half, Zamasu.