Also, I noticed that all the lounge chairs on the decks have a notice saying that you can not reserve chairs. So if someone complains that you took "their" chair you can point to the sign...
I did not see any problems with people saving chairs and not using them.... Most chairs had shoes, towels and bags and you knew that people were actually using them. I did not see too many chairs that had just towels... We had no problems finding a spot to sit on deck 10 but our kids are older so I did not feel like I had to sit poolside where it was not impossible to find a seat, but you had to wait a bit. The area around the pools is not all the big. (This was Freeport day, I expect that the cruises with a day at sea would be very crowded )