I think it all depends on a few variables to the individual...
-Do they base a lot of their income on guest posing year round, and need to stay in 'reasonable' shape
-How much water they actually drop on contest day (this can be a huge addition to how much they actually weigh)
-How long they've been training, and if they believe that being heavier will allow them to train better (heavier, harder) in the offseason (I think a lot of today's pros realize that you don't have to blow up so much in order to make progress)
-Injuries, and if letting their weight creep too high reaggravates them
-How much PEDs they use when not in contest mode (ie. Levrone being so much smaller when not in prep mode)
THere's probably a lot more, but these are just thoughts off the top of my head.