Originally Posted by
DarkenedHue
They are different roles entirely, suited to different purposes. At its core, Holy, like every other non-Priest healing class, is about replenishing lost health and keeping people's HP bars topped. Disc's damage-prevention through its extensive shielding on the other hand is something no other healing spec has a comparable equivalent to. It tends to be easier to swap a Hpriest out with any other healer than it is to replace a Disc Priest. That's why pugs and guilds on Icecrown tend to favour Disc priests. That said, Holy is more than viable in its own right, so just play whatever appeals to you more.