The obvious use for this is helping to block teammates in multiplayer, but it's incredible even in single-player, letting you ignore minions and extra attacks. Including those triggered by Taunts.

And funny enough, you don't even need to block the attacker. You can use this on a Pinned Down minion to ready, and then take the no damage from the attack.

IMO, this is a better card for ally-less Protection builds than Ronin.