Is there any use to the slide bounce/kick move?
As a casual player, the slide kick isn't much more than a way to attack while running. As a speedrunner/special-runner (e.g. A-button challenge), it's an invaluable part of Mario's movement abilities that lets him bounce in specific ways, cross gaps without jumping, and some other zany tricks.
On the other hand I don't think there is any practical use for the crouching kick aside from existing so the button combination does something.