The idea is you only have to paint correct the whole car ONCE. Even brand new cars from the dealership have shipping/industrial crap and/or swirls all over them with zero mileage on the odometer.
But once you have done this paint correction, then you only touch the paint using proper technique and equipment. This keeps your paint looking beautiful. You shouldn't have to clay or polish anything except small areas when something like bird crap or a light scratch happens. Light touch ups done properly could probably be done for the life of the car.
All that said, the answer to your question, it probably depends on the product/pad you're using. A light cut will allow you to polish a lot more than a heavier cut. The whole car can probably handle several heavy cut polishes, but ideally you don't ever come close to worrying about it
