This is a good way to make sure the mob is always attacking your pet if used liberally.
This can help you grab aggro off of another player if you need to
Stuns target, especially useful in PvP. In PvE, when applied at the right time, can help a player tank regain aggro. This is especially true when an enemy switches target to the hunter, another ranged dps, or the healer. A quick intimidation will not only switch the target of the enemy to the pet, but also keep the enemy close to the tank to regain aggro.
Patch 3.3.0 (2009-12-08): If the hunter's pet is in melee range of its target, the stun from Intimidation will now be applied immediately instead of on the pet's next swing or attack.
Edit
Patch 3.3.0 (2009-12-08): If the hunter's pet is in melee range of its target, the stun from Intimidation will now be applied immediately instead of on the pet's next swing or attack. 
