"Resting" the equipment and energy/cost efficiency.
Why run your equipment if it's not necessary?
Of course it won't make a huge difference is you have a handful of animals however when you have more than a handful it does.
But when the temps are actually warm enough the flexwatt will be off anyway. And if it gets too cold it will kick back in until it warms back up. You will save on energy costs either way.
So my goal would be to keep my flex watt set to my desired hot side temps and then keep the room temp as close to 84/85 as I can with using a fan to cool the room a bit in the heat of summer.