Except for when you're in the basement, away from the kitchen, one room over from the room in which your butterfly knife resides.
Honestly, I'm not arguing that it makes sense to buy a butterfly knife specifically to use for stuff like that, but if you do happen to have one, that can be a convenient use for it. They're more for collection value and learning tricks, which isn't any less stupid than learning card shuffling tricks or how to flip poker chips.
Also, before I borrowed it, my friend once used his to break into his car by prying the little side window open. Not saying it's the smartest use, though.