I put it on when I do jumping, but frankly it's only for the look, for me it doesn't carry any purpose (well, I have a strap there to hold if I can't hold myself, but so far I haven't used it yet).
I used to always ride with mine, but that was because my saddle was too narrow and would slide back really easily. I have a much better fitting saddle now and I haven't ridden any sort of steep hills so I haven't needed it.