Poison Powder isn't as useful on Butterfree because it walls like a sheet of paper. Sleep Powder will make short battles and catching Pokmon a lot easier, while Stun Spore will slow an enemy down for your slower teammates. i'm still kinda new with the whole nature and EV's and i'm not familiar with all of the moves in the game, nevermind all nearly 400 pokemon. Poison Powder is useless, Toxic is much better. I just started on FR and LG so if i appear like a noob it's because i kinda am, eventhough i mastered RBY. butterfree is probably not the best of pokemon, but i think with the right movesets he can be at least decent. Poison Powder is useless, Toxic is much better.
for one reason or another most people probably leave him in the storage after they capture some rares/legendary/OU but who can blame them.
we're talking full evolution and confusion at level 10.
I don't think many people use butterfree probably because of its crappy stats, but i've always been quite fond of it because he's easy to raise and he appears at the beginning of games and evolves early and gives you instant offense when you're starting a new game.