Let me explain when TO use it as a tank.
If there is a caster mob out of a group, toss it back into the group.
If there is sleep going on... dunno why there would be, but for sake of the argument... have the tank move the pack away from the sleep so overpowers don't wake it up. Then boot the thing into the pack as a wakeup call when the time is right.
Otherwise, don't move my mobs around on me.
Simple?