I was going to sell my filter pedal because I wasn't using it, but I joined a funk band and now I need both the wah and filter for different things.
I use wah for the "gwahk-a-qwahk-a meow meeeeow."
I use filter for that "bucka-byow-byow-bucka-braack."
See?
Sorry if this is too technical of an answer.