It depends on the restaurant you are making ADR's for. Some of the very popular restaurants require a credit card hold when you make the reservation. They do this in the event you don't show up and don't cancel before hand.
You will have to give your cc info for the signature restaurants and the restaurants that have character meals. Also, Cinderella's Royal Table and the dinner shows require full pre-payment when you make the reservation. At CRT and the dinner shows if you have a dining plan and link it to the res, you will not have to pre-pay, but you will still have to give the cc info for the no show guarantee.
Here's a list of the restaurants that require cc info: