Since this is in-game it doesn't matter what you use THAT much, But...
Butterfree can be good, Because in the early game, It's quite a good Pokémon with Bug/Flying STAB, A decent-ish movepool and it's Powder moves at that point in the game, And it evolves quickly. But in the later game, It's stats aren't as good as most other wild Pokémon / Trainers, And it won't be that good in battle anymore (It's still useable, Though). It doesn't help against many Gym Leaders either, Besides Olympia and Ramos, Though if it can take a hit it can be good against Korrina with Gust and Psybeam.
And while facing the Elite Four it won't be very helpful either, Since it's frail and gets outsped a lot.
So, In the end I would not keep Butterfree on your team. If you still want a bug type, You should use Scizor, Galvantula, Scolipede or Yanmega In my opinion. There are other good bugs out there, Though!
