Somebody saved a bit of money here at the time. The En-suite needed a new ceiling so they got the plasterer in to overboard it. Instead of getting an electrician in also for a few pounds, they had the plasterer cut round the fan leaving it in place.
In time the fan packed in and we were called. It needed replacing but that model is obsolete and cannot find one to fill the hole. Also cannot get the old one off as the cover screw on the side is now submerged in plaster, and the cover needs a slight sideways movement.
Cost the client more in the long run than just doing the job right in the first place!