The Prince is in a larger stall (12' x 20') at the barn where I currently board. We call it his penthouse apartment He loves it! He has plenty of room to lay down, roll around, etc. He does not trash the stall because he has more room. He is not the neatest horse, but he is not a pig either. In fact, the larger stall may have had made him a little bit better stall keeper
The Prince is 20 this year, so the bigger stall keeps him from getting as stiff with the old creaks and cracks. I think the bigger stall is really a benefit for the older horse.
The barn owner converted a cattle barn for horse use, so some of the stalls were off-sized in a smaller way. She didn't feel comfortable putting him (at 16.3) in one of the smaller stalls, so he is in the penthouse. She left a broodmare stall when she set up the barn and he is in that one. I really can't see a downside to having a bigger stall.