No other talent in the history of World of Warcraft has caused so much controversy and discussion like Circle of Healing, the 41 point talent of the Holy Priest. When this talent was introduced in patch 2.0, prior to the Burning Crusade, it was hardly considered viable. It seemed to be very situational and one had to give up the spirit buff from the Discipline tree, which made this sacrifice not worth it. Once you had entered the tier 5 raid dungeons however, the true power of the talent came to show and some guilds made on lottery which Priest had to spec the spirit buff and will not be able to use Circle of Healing. In fact some guilds even used a pure buff Priest for spirit, who would only buff the raid and then stay outside of the dungeon. The reason for this were bosses with massive raid damage, especially in Sunwell Plateau, which made AoE- and group heals mandatory, which only Priests and Shamans were able to cover.
This had the disadvantage that groups had to be built with circle of Healing in mind. The spell only has a limited range from the target it hits, so you had to take care that everyone in that group was close to each other. This often lead to raidgroup only containing five melee DPS, as that was exactly one group.
In order to ease this burden of group composition patch 3.0 made the spell intelligent. It now automatically selects the closest targets with the lowest amount of health left within range. Additionally a glyph was introduced increasing the total number of targets hit to 6. This change made the spell way too strong though. In some raids almost 90% of a Priests healing was provided by Circle of Healing. This was when Blizzard saw the need to step in. They added a 6 second cooldown to the spell, so Priests would be forced to use some other spells, of which the Priest has a wide variety. Although there was a huge uproar when this change was introduced the change went through, and despite the doomsayers the Priest remains a strong healing class, and with Prayer of Healing now able to target other groups they are still a capable group healer.