I think an issue that might come up that has nothing to do with the rate of the room is occupancy. When we booked the cruise we're going on next month, originally there were only 3 of us. But then another friend asked to come with us and we had our
travel agent add her to our reservation. The stateroom we were in could have 4 people sleeping in it but that category/section had sold out and no more guests could be added to it. I'm assuming it's a safety reason. I haven't seen anyone else mention that so maybe it's not something that happens often though.