The Global Cooldown (GCD) is the 1.5 second down-time after casting during which your abilities cycle around and are unavailable. This mechanic prevents super-macros and “mods” or “bot” programs from hyper-spamming abilities in an unbalanced way.
An example of this is the Auras.
All auras are attached to the Global Cooldown, and trigger it when you switch between them (though note that you can right-click it off your buff bar instead to cancel your current one without causing the GCD).
If Auras were unaffected by the GCD, consider this potential possibility:
If a Paladin were fighting a mob with a 2.0 attack speed, they know they will only be getting hit every 2.0 seconds. Without the GCD on Auras, a program or macro could be created that causes the Paladin to switch to Devotion Aura for extra armor a split second before getting hit, and then switching back to Sanctity Aura for increased damage immediately afterwards. They could keep doing such a switch over and over in response to every attack.
Auras unattached to the GCD would effectively create the potential to gain the effect of multiple auras at the same time. This would be unbalanced and unfair by any stretch of the imagination, especially as such a tactic would require rather conscious exploitation of the mechanic and isn’t something normal player reflexes would be able to accomplish, which distinguishes between a strategic facet of the class and an exploit of mechanics.
For tanks, the GCD is extremely important, and managing it is a skill in itself.
Gestalt had this to say about the subject:
Q u o t e:
With the exception of Judgment, all Paladin spells and skills [used in tanking] activate the Global Cooldown. Given that most of the spells used for tanking are instants, the Paladin has no method of “soaking” the downtime between GCD’s [such as Heroic Strike for Warriors]: this built in pause is a true pause.
The Paladin offsets this with the duration of all their GCD-consuming effects: most Paladin tank spells are fire-and-forget, something you can activate then simply allow it to work for a few seconds. The moderate cooldowns on most of these spells means the Paladin will rarely have to choose between more than 2 or 3 abilities on any given Global Cooldown.
A Paladin will have to choose carefully to optimize their efficiency, unless…
Unless they don’t have to choose at all.
The Cooldowns for the primary tanking spells can be staggered in such a way that they will rarely, if ever, overlap. Your initial series of casts throughout a fight will determine how frequently this overlap will occur: if you start out with a string that brings an early overlap, you will have to deal with those overlaps frequently. If you start out with effective staggering, you will only have to maintain it.
The one curveball you will have to deal with is long cooldown skills, like HoJ, or long fights where reapplying BoSa is necessary. There are a few tricks that help in this process:
-use Consecrate before Holy Shield any time you’ll be using both. The 2 second gap between their CD’s means that if you reverse this, they’ll overlap on the next CD.
-The time when both HS and Consecrate are on Cooldown is when you Judge. While Judgment itself does not invoke GCD, the seal you’ll be refreshing will.
-Special or situational abilities like HoJ, AS, or refreshing BoSa should also be fit into this window, but be aware of how this may affect the timing of other skills.
-Keep an eye on your cooldowns. If you aren’t using a mod that displays the cooldowns on the buttons themselves, get one.
-Keep an eye on your spell durations. Turning on “Aura Fade” for scrolling combat text will give you a visual cue when seals and blessings fade, but you need to be thinking ahead so you can fit refreshed buffing into your skill rotation.
(Credit: Gestalt, Ysera)