Allows you to give the customer a discount, write it as bonuses in the future to accept payment of these bonuses. Or in other words, if you pay the check, the customer is given a discount, but it is written in his "account", and the check is paid in full.
Such a system is in demand, many buyers like it, you will agree, it's nice sometimes to buy something in the store, "without money."
How to use power-ups, I have written in the form of presentation (below), so more clearly. If you are uncomfortable to watch a presentation on the website, you can download and view it on your computer: