I think it's incredibly important. As was stated above though, I agree that stressing over fractions of degrees is unnecessary. Keep your husbandry correct and consistent for the animal in question and things will be alright. Also I think it's important to be in tune with your animal's behavior because that's what will tell you when something is wrong. I've def been guilty of checking temps 30 times a day and obsessing over every little detail. I think it's easy to forget these are animals that normally live outside and some environmental fluctuation is ok.