If you ask a random D&D player what a cleric does, five out of six of them probably say, “A cleric heals.”
A simple enough statement, but the cleric’s ability to cast cure light wounds and similar spells injects a bit of tension into the game, which essentially boils down to how much of her own resources the cleric should expend to heal a friend at the expense of doing something else (such as attacking the monster with her mace or casting a searing light spell).
In earlier editions, a cleric had to devote precious memorization slots to curing spells. This meant that a cleric who didn’t want to be bothered with healing friends would choose few or no curing spells—end of discussion. Whereas a cleric who memorized curing spells knew exactly what she was getting into (and humorously enough, around a few gaming tables I’ve heard about, charged friends for the privilege of receiving those spells).
In 3rd edition, we saw some relief to this tension due to spontaneous casting, which allowed a cleric to trade any memorized spell with a curing spell of equal level. This was a useful advance, though some tension remained because the cleric who cast a curing spell on her turn was doing that instead of taking some other action.
The 4th edition rules focused on the opportunity cost of spending an action to cast a healing spell, and, with the healing word power, gave clerics curing they could use twice per fight so quickly that they could still take the rest of their turn normally. This cleric healing rule removed almost all the tension from choosing to heal friends (especially in association with the healing surge concept, character-triggered second winds, and expanded secondary class healing).
So that’s the quick rundown, which leads to my question.