This talent heals you when you take damage. As it is in the Fury tree, it would only be useful to a Fury Warrior while solo leveling, as in groups they shouldn't be taking damage. As a tank, (minimum level to be able to reach it being level 71) it is very useful near the end of your leveling and into dungeon running, reducing the strain of the healer's mana.
As of unknown patch before January 4 2001, has a 10% chance to regenerate 1/2/3% of your total health health over 5 seconds after taking any damage.
/Patch 4.0.1 (2010-10-12): Completely redone. Now has a 10% chance to regenerate 2.5/5/7.5% of your total health over 5 seconds when affected by an attack.
Patch 3.0.2 (2008-10-14): Now regenerates 2/4/6% of total health over 6 seconds.
Patch 1.5.0 (2005-06-07): Talent design changed. It now regenerates 1/2/3% of the warrior's total health over 6 seconds after being the victim of a critical strike.