The Hand of Protection (HoP) is a valuable tool in the pocket of every Big Healing Paladin. It can save the life of a aggro pulling toon with a quick immunity from all physical damage. The mob will turn in disgust back to the tank, just waiting for the Protection to end. I can't count the number of times I've HoP'ed a caster who pulled aggro on a big AoE pull. It's not unusual for my HoP to hit right as they Ice Block or Soul Shatter. Too bad most mages don't know how to cancel their own ice block (hint: cancelaura Ice Block, macro it to the same key that ice blocks, hit once to block, hit again unblock) to take advantage of it. I've also saved a lot of Fan of Knives crazy rogues. The rogues usually don't like it because it prevents them from doing damage until they remove it or it ends. For a paladin it's a must have tool, since it can quickly save the life of DPS or Healer that suddenly has aggro. I practically use it on every CD during the Faction Champion encounter.
Don't wait for special occasion to pass out this protection. Often there isn't a lot time between getting aggro and getting dead. I tend to HoP quickly and often.
The HoP can also be used to clear of some debuffs. Cast HoP, then quickly cast Hand of Freedom (HoF). Since a player can only have a single Hand on them, the freedom will immediately clear the HoP off of them.
Just remember it only protects physical damage, if the attacks are magically, they will need Big Heals instead.