Vanilla Blood Flow is 0.5s cast time 3s cooldown
3/3 in this feat and it becomes:
0.5s cast time, No cooldown.
Probably works the same for the other 2 priests HoT.
Bear Shaman Related
Getting 3/3 has synergy with Balance Of Nature, as you can spam Blood Flow quicker until Balance of Nature procs and also has synergy with the Blood Warrior feat, as you can spam Blood Flow 5 times in only 2.5s rather than 15s.
Don't know if these synergies are worth getting though and also spamming Blood Flow every 0.5s can apparently cause lag.