It's been so long since i saw "Tree of might." I know the spirit bomb did fuck all against Freiza. I think Goku may have killed Turles with it.
Yeah..but The Tree of Might and Turles aren't Canon. @_@
I mean, he used it against Majin Buu, and it kind of made a dent in him..sorta.
Anyway, we all know that Dragonball Z was supposed to end after the Freeza Saga, and they just kept demanding more.
I mean come on, it's the perfect setup for an ending, Goku defeats Freeza, the most powerful, evil being in the universe, dies saving his son and family from Freeza's threat, and Gohan goes on to live a normal life.
Then the Cell Saga comes along. Goku defeats Cell, leaving Gohan easily capable of defending the earth on his own from any more threats, aswell as securing him a mostly peaceful life, aside from the Tournaments.
Then Majin Buu comes along. @_@ Goku is like "Ok, why the hell do you people keep coming back?" kill Kid Buu, Gohan is left the strongest in the universe (Literally, THE strongest) Goku passes on, leaving Gohan to defend the earth as the strongest being alive.
Then GT comes along and Toriyama was like "No, Fuck you!" And did some concept sketches before walking out. @_@