The periodic portion of lifebloom stacks up to 3 times, the bloom does not, so if you cast a single lifebloom and constantly allow it to bloom, you get a really weak 7-10 sec duration hot with a moderate heal at the end (3k+ish), however if you set up a rolling lifebloom the periodic portion becomes a fairly substantial hot that is quite cheap to maintain (only 1 gcd every 10 secs). If you are allowing it to bloom constantly I really hope you aren't stacking it to full (that would be a constant 3 gcds over a 10 sec window assuming you run with minimal duration LB). When you consider the HPM (heal per mana) and HPCT (heal per cast time) impacts rolling lifeblooms works much better.

That said with the 3.1 changes who knows what'll happen.

okay I didn't know that. One more question,

So suppose I cast lifebloom at time 0:01, time 0:02, and time 0:03, and then the third lifebloom will go all the way to time 0:10. But what about the first lifebloom, does it go to time 0:10 second or just 0:07? That means on 0:08 am I left with 2 stacks or still 3 stacks?

And if I cast one at 0:09, does that refresh the timing of all 3 stacks?

If yes, then I see why rolling is much better because then the "bloom" will delete all 3 stacks and you have to cast 3 times again. So in this case the bloom is more for pvp usage in case it gets dispelled I guess.