We had to purchase an extra room due to my daughter coming on the cruise with us. We have a balcony room with sleeper sofa and the room capacity is four people, but RCCL says regulations only permit a certain number of triple/quad occupancy rooms and they are at maximum so we could not add a third person to our existing balcony room reservation and had to buy an extra room.
The extra room is an interior room on the 9th deck (#9611) and will be completely vacant and unused since the three of us will be in the balcony room. I can add one person to this interior room and that person will have the room to him/herself. Price $750 (a little less than half of what I paid for the room).