I fully admit I let my tanks get to 50% or less because I'm putting dots on, then I switch out of CS and heal them to full. I've had tanks cure themselves (GLA/PLDs) and THM/BLM or ACNs Cure/Physick them. But as someone who mains tank I know how much damage they can take and as someone who's been running all three healing jobs at 60 I have a pretty good grasp of when to heal and when to dps.