Blessing of Sacrifice can be used to avoid being the victim of Crowd Control in PvP. Bless a person who is quite likely to draw enemy fire. This way, if you're afflicted by Polymorph, Sap, Repentance or any other of incapacitating effect, the damage transferred to you would break Crowd Control.
Blessing of Sacrifice can be useful in PvE when tanking mobs that fear in 5-man instances, such as the Fel Overseer in Shadow Labyrinth. If you put Blessing of Sacrifice on a party member, you now will not get feared, but them getting hit will break your own fear.
Blessing of Sacrifice can be very helpful when tanking Blackheart the Inciter, especially during his 'incite chaos' spell to take damage away from all party members, and also for picking him up after his 'incite chaos' spell wears off. NOTE: This will probably be less feasible with the 2.2 patch changes to Blessing of Protection.
Critical during the Maiden of Virtue fight in Karazhan, allowing paladin healers to be awake during the Maiden's Repentance. All of the paladin healers should keep Blessing of Sacrifice activated on the tank and melee DPS. Decide before the fight on who to bless whom, as it cannot be cast on the same player by two paladins.
Note that using Blessing of Sacrifice may make it difficult for the healer to heal. Normally, the healer would only need to heal one target. Under Blessing of Sacrifice, both you and the player you blessed would take damage. Be sure to communicate this to the main healer, and do try to heal yourself from your own mana pool if it is feasible.
For Retribution Paladins, this blessing can be used to counteract the change to Spiritual Attunement that took place in patch 2.1.0 (Overhealing will no longer trigger Spiritual Attunement's mana regen), restoring much of the synergy that takes place between a Retribution Paladin and a Shadow Priest, but at the cost of being unable to cast another blessing on the tank. It is up to you to decide whether you want to bless the tank or have more mana.