We use ours for many things:
Gratuities (DSC)
Upgrade Beverage Package
Upgrade Interent Package
Extra Specialty Dining
Bingo
Paint at Sea
Don't forget you can get your refundable OBC back in cash when you disembark. I didn't know this last cruise, but when I scanned by pass to get off the ship, they told me I had to go back and see the cashier. I had $84 left and they would not let me get off without cashing out first. Now I know better and will stop by the cashier before getting off the ship.