In the World of Warcraft, there are some instances individuals take a role proceed to redefine it into "non-traditional" role. For example, there is the player that decided to level without killing anything, or the hunter that decided not to level ranged weapons at all, but instead maxed out melee. These people are proof that your characters are flexible, unique, and can fill roles that others would not immediately think of.
   Along these same lines are character builds that involve or ignore talents and spells that others find key. Speaking specifically of the new Penance spell that all of the Discipline priests have are just gaga over. However, while it might be an efficient spell depending on how you use it. It is said that a Discipline priest must have it in order to be a viable party/raid healer.
   Stop Assuming you need it - Yeah, it's a 51-point spell. But do all Beast Mastery Hunters use Beast Mastery? It's not too long ago that Lightwell was at the top of the Holy Priest's tree, but did anyone actually use it? Taking a talent without making sure that you will use it efficiently is useless.
  Regarding to Dual Tasking, let's be honest, Priests are not hybrid classes. We're not meant to do both healing and damage at the same time. We really get to pick one or the other. We do a good job at either one such as nice shadow Priest, good shadow Priests. But at the same time, both are impractical or inefficient. So a spell that can either do heals or DPS depending on who is targeted?
This can be a big problem.
There are only two other spells that we have that works like this: Holy Nova and Dispel Magic. However, the priest that considers Holy Nova a crucial part of his healing spells needs a reality check, and Dispel Magic (and Mass Dispel, fine) is not going to be an issue if it's cast on the wrong target (unless you really had to dispel a DoT or effect off of a player and you miss).
Let us not forget Mr. Urkel and his occasional mistakes with such horrible results. Imagine that you go to heal someone in your party, without realizing that you have a mob targeted that has not yet been pulled. Oops…not only are you making new friends fast, but your tank probably won't have time to pull it off of you. Any other heals and this would not be a problem - in fact, the inability to use healing spells on enemies can help you.
The hell does that mean which is a trick that I used to use in Hyjal and Kara. Target a mob that you have to shackle and after they're shackled, leave them targeted. When you click your keyboard buttons for heals, the system will try to heal your target. You have an enemy targeted, so it will instead give you the "grayed-out finger" pointer. Then, just click on your healing target. It's a click tap-click to healing someone. The advantages are that you have no need to use a focus and you can still pick up the shack quickly if it breaks but the disadvantages are that slightly slower than normal, takes a little getting used to, will not work with Dispel Magic or Penance.
When the GMs build spells, they do it with careful consideration to effect intensity, cool-down, casting time, mana cost, and reagent cost. If they did not, you'd see Instant 50,000 damage spells that cost 100 mana with a .5 second cool-down. No, every spell that they give is balanced through the various aspects. And when it comes to pure healing spells, cool-downs can be death. Waiting for heal to be available - or, rather, heal that so many people think is just "so awesome" is a crapshoot. If a six-second cool-down can kill Circle of Healing, how is Penance so great with a ten-second cool-down?