using american express for sail and sign, question?

I just was reading on the facts and questions for carnivals website on using the sail and sign card. on that section, it said if you present your credit card they would put a hold on that card until the end of the cruise and that it would limit your use of that card for other things and purchases. i am assuming they mean when you get off of the ship and want to purchase things on the island such as food or souvenirs you may have a problem. i really did not understand their meaning of hold on the card and limit other purchases. could someone explain this to me. thanks

[ROXTEACHER]

I used my Amex card (the only one I have/use) for the Sign and Sail and had no problems and no "limits" were placed on my account. I assume that if you use a true credit card (MC, Visa, etc.) CCL will check to see what the credit limit is and what available credit remains. Since AMEX allows one to charge based on previous charge history and payment history, you should be fine as well.

I've used AX on all my cruises since 1985 and never had a problem charging anything either on or of the ship