Only other reason I can think of (and it isn't that good of a reason), is that say you have a BE and your hand is full, but you want to use mindgate or golden hourglass to get another card, but you can't because you have 8. Maybe you need to dump your BE, and you have a cocoon on the field. Wouldn't it be nice if it turned it into a butterfly?
Yeah, but I think it isn't necessary to add that effect.