WARNING: The following article contains spoilers for Dragon Ball Super Chapter 78, "Gas's Wish," by Akira Toriyama, Toyotarou, Caleb Cook and Brandon Bovia, available now in English through Viz Media.
Dragon Ball's Vegeta isn't known for emotional outbursts during fights. He comes off as cold and shut off from others emotionally. One thing he does feel, however, is regret. As the Prince of Saiyans, Vegeta felt it was his duty to avenge the loss of his father and his people at the hands of Frieza. He lost not only his home, but his family and his legacy. Vegeta would be robbed of this vengeance when Frieza proved too powerful for him and Goku was able to achieve the Super Saiyan form before he could. It was one of the few times fans have seen Vegeta shed tears.
Ever since then, Vegeta has pushed himself to be better than Goku, to be stronger than Goku. He is fueled by his regret over not being the one to take out Frieza, fueled by the need to prove his worth as a prince. Vegeta lost everything to Frieza and to have someone from a lower class of Saiyan warrior surpass him ultimately defeat the tyrant is probably the thing he regrets the most in his life. He never got the satisfaction of winning that battle. But, in Chapter 78 of Dragon Ball Super, Vegeta takes the opportunity to spare Granolah the same fate.
Granolah's sole motivation is to avenge the death of his mother and his people. He was willing to do anything to achieve this goal, but it all came crumbling down when the Heeters used the Cerealian Dragon Balls to turn Gas into the strongest fighter in the universe. Now, Granolah barely has the strength to sit up. However, Vegeta has a plan to help the Cerealian take his vengeance.
At Goku's behest, Vegeta retrieved the Senzu Bean from his armor, but he decided against eating it himself. Instead, he urges Granolah to eat the bean and use his own strength to get his revenge. He doesn't want Granolah to experience the same regret he has felt for years. Vegeta wants Granolah to push himself and achieve what he couldn't with Freiza.
The battle against the Heeters is one Vegeta knows isn't his to win. He had no real stake in this until Granolah targeted him and Goku. But he sees himself in Granolah -- an angry shell of a man fueled by nothing but rage and vengeance. Should Granolah not fight and the Heeters be defeated by someone else, he will never receive the closure he needs to move on with his life.
Vegeta was lucky in that he found a home and found a family to call his own. He knows from experience that it's hard to find a new purpose in life once your sole reason for living has been taken from you. But Granolah may not be as lucky as Vegeta was and, if he doesn't beat the Heeters himself, he will likely never feel complete. Vegeta sees much of himself in Granolah, and he clearly understands how someone like him will react should they not fulfill their sole desire in life. That is why he gives Granolah the Senzu Bean. This is Granolah's fight, not Vegeta's.
