While the mana cost reduction may seem small at first, it adds up to a large amount of mana saved, especially in raid encounters where fights are often very long. This is also the only talent in the Restoration tree that affects the mana costs of healingspells.
/Patch 4.0.1 (12-Oct-2010): Reduced from 5 to 3 ranks, mana cost reduction changed from 1/2/3/4/5% to 2/4/6%. Moved from tier 2 to tier 1.
/Patch 3.0.2 (14-Oct-2008): Moved from Tier 1 to Tier 2.