First, unless you have the MYW +Premium Dining (which you may) you will use 2 table dining options for HDDR. If it is Premium then it may just be one. Make sure of this before you leave so that you do not get to WDW thinking you have one more table service than you actually have.
Second, the credit card is to assure the HDDR staff of your intent. If you do not show up they have several options. #1 - they will charge the dinner fees to the card and leave your table service options alone. #2 - they can charge you your table service options and leave your credit card alone. #3 - They will charge both and you will lose money and table service options. From what I gather from the Dining CRO is that #2 is the most likely to happen.