Its all situational. In CM during certain bosses...there are what some 7 adds to spawn at times during bosses? A regen on a tank will put hate on you generally if they can't grab aggro on them right away. During bosses that hit pretty hard, well the regen helps out quite a bit. Especially during Coil, Turn 1/2. Now during 4 I only use it during certain times before I know enemies won't spawn and I won't pull hate. I myself use it quite a bit, but give the tank some time to grab a little hate before you do so. There is no reason to cast it right away.

During Ifrit I always have it up. Same with Titan. Now Garuda, I'll hold off until the sisters die and I'm sure not to use it or have it up before they do. If you're doing fine so far or already know when to cast there is not much more I need to tell you. Always keep an eye on the enemies aggro and wait a little if you have to if you get into orange to heal again.