All i think you can do with ducking is duck jump and dancing and a long time ago a sweep kick. But is there anything else its used for in this game?
You can lay the eggs on the branch at the bandits.
You can take imaginary poops.
It actually does shorten your hitbox a bit, but usually not significantly enough to help dodge anything, except maybe in the rare scenario your already on a lower plane than your opponent. Otherwise mostly just for duck jumping and dancing etc. haha. It will likely be more useful in V3 though.
Can't forget the ability to give people surprise buttsex.
Teabags. Which is like what Lucifer said.
It helps a lot for pvp on the arena steps as I have found out.