All of the usual banking deadlines apply even if you are waitlisted. So if you decide NOT to bank your points and continue on the waitlist past your banking deadlines, you would have to use the points before the end of your use year even if the waitlist didn't work for you. In this situation, some people bank their current use year points and then if the waitlist comes through, they have MS borrow points from the next use year to complete the reservation.
Any banked points must be used by the end of the use year that they were "banked into", so be sure if you try the above (because you're not sure the waitlist will come through for you), that you have a plan to use the points for sure in the next use year. If you don't you will lose them.
Hope that made sense. Not sure I explained it very well.