Well the problem with DBZ is that, compared to Goku, EVERYONE is a useless idiot...and in the case of the Buu saga, even Goku was a useless idiot in that he didn't kill Fat Buu when he had the chance because he wanted everyone else to have a chance at saving the world. Well, come to find out when you leave the world in the hands of a bunch of useless idiots who have been watching you do all the hard work in saga after saga after saga, the world's population gets killed and eventually the planet gets destroyed. Smooth move, Exlax.
Buuuuut in more practical terms, Future Trunks manages to kill off Robo-Frieza, preventing him from causing havoc for 6 hours before Goku would have shown up and beat his ass anyways. But beyond that he gives Goku the medicine needed to combat the heart disease that apparently would have killed him. So it can be argued that he saved the hero's life so that he could, in turn, save everyone else's life.
After that though, yeah, he might as well change his name to Krillin like everyone else.
Edit: To head off everyone saying "Nuh-uhhh! Gohan killed Cell!" Yeah, and he would have just rolled over and died if his father wasn't there pushing him all the way till the very end of the fight via telepathic communication. And depending on your interpretation of Goku's image flashing behind Gohan for the "Father-Son Kamehame" that finally kills Cell, it could be argued that Goku LITERALLY helps him with that final attack...nevermind the fact that all the other worthless weenies had to keep attacking Cell to distract him so that Gohan could get that final push in to begin with.
Edit Edit:
DoPo said:
Who is Kanenshuu? What colour is USSJ??
Also: this.