Well let me see if I can explain this.
Basically you have to first decide if you will be leaving a credit card at check in for room charging. If you do, then you can do express check out and they will just charge the card you leave the morning (very early) of your check out date (or whenever you hit the predetermined limit, I think it's $500 for All Stars, then they will charge it again for the rest of the charges that morning). If you decide to do this, then they just hang the bill from your door and you are free to just leave by the check out time.
If you would rather leave cash, travelers checks or whatever, the same thing applies. They will give your room that amount of credit, and if any $$ is due back to you, then stop by the desk and pick it up before leaving.
Or you can leave the credit card, and then go pay any way you would prefer, the night before, and then also leave after they leave the bill (which if you paid the night before would have a $0 balance unless you charged to the room after you paid it off) on your door.
If you don't plan on doing any of the above, you will have a $0 balance on you room and your stop at check-in on your way out will only take a minute. I hope this helped!