I believe they just run your card thru, to make sure it is valid. The limit depends on where you are staying. $500/value $1000/moderate, and I'm not sure about the deluxe.
Anyway, once you have reached that amount they charge your card, and you start over again. If you don't want your card charged, you may leave cash at check in or you can go to desk before you reach your limit, and pay it off.
At least this is how I understand it. I used a debit card last trip, and I know they charged nothing to it, until the end of our stay. Actually the morning we checked out. We could still charge back to our room, our check out day. They ran a second charge thru, at the end of our check out day.
Hope this helps.