While on the Adventure OTS last year, I pre-reserved our specialty dining and my credit card was charged ahead of time. They also charged my card for the pre-reserved shore excursions. I don't mind that, if I can pay for that ahead of time, then it keeps my onboard account a little lower and that makes my wife happy! I know you pay for it either way, but my wife freaks out at the end of every cruise when we get the onboard bill the morning of departure, even though she is the biggest spender of the two of us! So the more I can prepay on RCI the better for me. On our upcoming RCI cruise to Europe next year, we will have $450 onboard credit, so with a lot of pre-reserving stuff like spa appointments, shore excursions and specialty dining, I'm hoping for a very low bill and less "Freak out" from the wife next year.
On our Princess cruise coming up, I pre-reserved a shore excursion and they did not take a credit card, just put it on our booking and will be charged to the onboard account.