The problem with no gradient is that you are assuming there is a sweet spot that the animal wants to be at all the time. First you have to be able to know and hit this temperature. Doesn't it make more sense to give an animal a gradient and let them figure out what temp they want to be at? Second you are assuming the animal wants to be at the same temperature all the time. You even admitted there are times when an animal benefits from being able to increase its temperature. Also as a bit of anecdotal evidence I often see all of my snakes on a hot spot of around 89 degrees, if they didn't appreciate these higher temps they would not be on this side.