I know people who make seasonal adjustments, it just sort of depends on what you find nice. Mostly I go for excessively hot water and most hot tubs are cooler than I'd like as it is. In super hot areas you can get chillers for the water instead of heaters.
I do make seasonal adjustments on my water bed! Like a water bed, the amount of water in a hot tub is a lot of mass and it is a lot of energy exchange over time, not a quick fix or change for more than a couple of degrees.
That is one of the things to look up is the heat up time, for energy savings mostly you keep the water a bit lower and then warm it up before use. You can get timers to cycle through cleaning or heating automatically.