This spell is very useful against melee attackers in PvE or against Warriors and Rogues in PvP.
Activate this spell when running away. Often the attacker will be rooted and unable to follow.
This spell is also useful for gaining range against a Shaman to use Innervate.
It is entirely impractical for raiding if the druid is not a tank, given that 1) the scariest mobs are immune and 2) the Druid shouldn't aggro away from a tank, 3) the Druid is not likely to survive a single hit, and 4) a rooted mob will turn to attack other people in range, regardless of aggro, potentially killing others in addition to the casting druid. There are, however, a rare few applications, for example when dealing with blood beasts in the Deathbringer Saurfang fight.
Can also be cast in Cat, Bear, Tree of Life, and Moonkin forms.