The reason for it as far as restaurants are concerned is in case a tip is added. When the card is first presented and entered into the terminal only the amount for the meal without tip is entered. The financial institution will put a hold on another 2O to 25% in case a tip is written in by the customer. Usually the tip amount isn't adjusted until the end of the shift or even the end of the business day when the batch is transmitted.
Hotels will put a hold on a certain dollar amount which will include the base amount of the room along with any incidentals such as phone calls, room charges for meals, etc. I believe they use a percentage of what the average stay is above the room charge but I'm not for sure.
Sorry if it seemed I was yelling at you Brandy, but I wasn't upset with you. I am also a consumer and this affects me as well. It just happens to be one of my pet peeves.