Regrowth has the worst mana efficiency from all of the druid's healing spells which made some players debated over the usefulness of this talent since it does not change the spell itself and requires 5 points to maximize.
However, druids in Tree of Life form should strongly consider this talent. Investing heavily into this talent boosts the critical chance by 50% which technically guarantees every second Regrowth a critical heal. This can dramatically improve both the health per mana (HMP) and health per second (HPS) efficiency of Regrowth, making it the ideal larger heal when instant cast heals like Swiftmend and Nature's Swiftness are not available.
Patch 3.1.0 (2009-04-14): Renamed to Nature's Bounty. The critical effect chance has been lowered from 10/20/30/40/50% to 5/10/15/20/25%. Nourish is now also affected by this talent.