Pretty much this. Lifebloom itself is super efficient (costs virtually zero mana, especially if you put up the 3 stacks before the fight starts) and does a fair amount of healing on that target. There is no reason not to take this, quite literally, free healing. Additionally, and perhaps even more importantly, it proc's our Omen of Clarity which means free Regrowths. This results in a few things. Most of those regrowths will be thrown into the active tank (who also has the LB stacks on him). This both refreshes the lifebloom for 0 mana, refreshes your mastery for 0 mana, provides a sizable critical heal to the tank, AND leaves a living seed on the tank for future damage.
Most of the time you will get at least 1-2 procs of OoC every 20 seconds (mastery and lifebloom duration), making both mastery and lifebloom easy and efficient to keep up.
Again, there is ZERO reason to avoid using lifebloom. It is literally FREE healing, on multiple levels. The only reason I can see for not using LB would be incompetence or laziness.