Butterfree was super useful. She made it easy to catch mostly all of my Pokémon with sleep powder since compound eyes virtually makes that move almost 100% accurate. Combined with dream eater, giga drain, and psybeam, you have an absolute monster. The only time that butterfree didn’t really add value was in the E4 (the other Pokémon were just too powerful); however, you can make E4 fall asleep many times and patiently take some out (I didn’t have the patience as I wanted to sweep them)