Last updated: 12/02/08, patch 3.0.2.
A defender of the light or champion of the darkness, all priests fall into essentially two categories: healers or ranged damage dealers.
Apart for some very special and bizarre circumstance, priests are not meant to be tanks, nor melee DPS.
A priest with the majority of their talent points in their “Shadow Magic” talent tree specialize in dishing out the damage to enemies. At higher levels, shadow priests gain a good amount of party/group utility by gaining spells that will let them do damage while regenerating their party’s health and mana and increase their group’s magic damage against enemies as well.
The one thing that perhaps sets shadow priests apart from other priests is the 31-point talent in their shadow tree: Shadowform. This gives the priest the ability to change form into a shadowy, purple version of their previous avatar, granting an increase in damage given and reduction in physical damage taken, but rendering them unable to cast any spell in the holy school.
Unfortunately, many non-priest players regard priests as healers and nothing more, so should you choose a damage (shadow) talent build, you may encounter some “lol priests r 4 hael n00b” attitudes. Do not be deterred, though: it is possible for shadow priests to out-damage other damage-dealing classes.
Many players level as a shadow priest for the ease of doing damage to their enemies. This leads to faster experience gains, and hence, faster leveling.
One of the strongest healers in the game, priests focused in healing are able to keep party members alive with ease.
Holy priests are considered to be the hybrid of the healer classes: paladins specialize in spamming heals to keep party member(s) alive, druids specialize in using heals-over-time (HoTs) to keep party members’ health stabilized, and shamans specialize in keeping their entire party alive with area of effect (AoE) group healing. Holy priests can do all three of these things well. This gives us great flexibility in end game raiding and keeps priest healers in high demand.
Priest healers specializing in the discipline tree instead of the holy tree focus more in damage prevention than raw healing power. This unique role makes them the ideal healers for tanks, the soakers of damage.