Contrary to what most of you have said, I don't believe that it's healthy for a male betta to flare all the time. Oh, it's true, it looks nice and pretty but is it really necessary? Do we only buy bettas to see them flaring or because we appreciate a beautiful fish that we allow to live in peace. It's a bit like parading your dog in front of other dogs just to make it bark all the time. In the wild they live a very lonely existence, some of them never even seeing another betta all their life and only flare when another male approaches (a "get out of my territory or else" flare or when a female approaches (a "come and see my nest" sort of flare) I personally believe that flaring stresses them and fish that are stressed all the time sometimes sucumb to disease easier than others that are calm and stress free.
Most of you most probably disagree with me, and, as I stated at the beginning, this is just my opinion.