Eye for an Eye, while not a great ability by itself, is GREAT when stacked up with other abilities. The trick is using it 20-30s before the big damage you're trying to prevent in the hopes the enemy(ies) get the debuff. Add Sacred Soil, Virus, and... The bard one... to the mix, and you have INSANE damage reduction.

On Garuda if I time it properly, nobody even gets to half health from reckoning. On Titan, I usually have a Summoner friend with me and we alternate Virus and Eye for Eye basically on cooldown, it can save the tank from a Mountain Buster, and greatly reduce the damage dealt by Tummults, especially if everyone is stacked in Sacred Soil. Since it's on a long-ish cooldown, its great for a WHM to have and the SCH can alternate casts in 8man content.