This is how I proceed as well, but the way you put it is a bit misleading those who would be tempted to try to dps more and end up tunnel-visionning, to whom I'll add this precision :
We do look at the tank HPs - constantly - and at the Damage dealers' HPs - constantly. We also look at the aoes on the ground, all the time, and we do have our eyes on a dangerous enemy or a boss' s castbar to predict when the damage is coming, to decide when and what type of healing is the most appropriate (if any) Besides that, we try to keep an eye out on Damage Dealers 's positionning as well, to precast a cure or anticipate a Tetra / Benison / Bene, if needs be.
This type of agressive healing is not something you wanna try "out of nowhere", in the middle of an expert dungeon. Instead, it's recommended to try at lower levels, and progressively get used to it, so that you can in the end reach that type of surgery-healing.