why do hotels need your credit card when you check in for a fully-prepaid room? for example, fully prepaid on hotel's website, priceline, hotwire, or any other travel website.

last week I checked into an airport Hyatt with a $50 AmEx gift card that I got from a CLF lightbulb rebate. Since I had the kids with me on this trip, I asked that PPV, room service and LD phone calls be blocked from the room, which the clerk did without saying anything.

I had no idea how the clerk was able to run an authorization, but she probably punched in only $50, since the card showed $0 available when I went up to the room. The authorization went away and the card had $50 available balance a few days after I checked out of the hotel room. Used up the $50 on groceries a day later.

When I checked out, my bill was zero, since my room had already been prepaid on Priceline for the 4-night stay.

So, what was the point of the hotel asking me for my credit card in the first place?