If you only have one credit card, or a small limit, be wary of registering a credit card for charging purposes. Upon check-in the hotel will obtain authorisation from the issuer (as Karen says, $500, $1000 and $1500 respectively in the case of Disney resorts). On check-out, they will charge the actual amount of your bill to your card. The chances of you spending exactly the amount authorised are somewhere south of nil, so the two won't match. The authorisation amount will then remain outstanding, reducing your available credit. It can take up to a month for outstanding authorisations to run off. [When authorisation is sought, the hotel will be given a reference number which they're then supposed to use when charging the actual amount to ensure that the two transactions are linked, but they seldom do.] As Karen points out, once you reach the authorised amount, the whole process starts all over again, so imagine this scenario for a Pop Century stay:
Your credit limit: $2000
You register your card for charging privileges upon check in. Pop obtains authorisation for $500.
You use your room key for charging all your meals and purchases.
At the beginning of day 4, your bill stands at $476.35. You go for breakfast at Boma and charge your bill of $72.75 to your room. Your total is now $549.10, so Pop charges this amount to your credit card and processes a further authorisation. The amount outstanding on your card is now $1549.10 (the original authorisation amount + the amount charged + the second authorisation amount), $1000 more than you've actually spent! I'm sure I don't need to go on.
I can understand the appeal of using your room key for charging privileges, but it's simply a credit card proxy. There aren't any benefits at all and, if you were to lose it, it could be used fraudulently in just the same way that a credit card or cash could.