Like other posters have said, its a crowd control skill. Its used to take other mobs out of the fight until the group is ready to kill it. As a shadow mine is only 6 seconds but its great if your current cc breaks and you need time to re cc the mob or kill the one you are currently fighting. If you spec into it in the balance tree it can also work like a 4th interrupt (mind snap, stun, knock back and lift).