History of Stagger
Due to the incredible unpopularity of Stamina Dragonknight DPS in raid teams due to their low sustain and DPS issues in recent years, the combat developers added a unique debuff to what they would designate as a Stamina Dragonknight spammable skill which was lambasted across the board by both PvP'ers and PvE'rs who wanted a different spammable aesthetic and skill that played to the class identity of the Dragonknight.
Stone Giant would offer the completely unique debuff called "Stagger" which would increase all sources of damage done by 45 per stack up to 3 times (total of 135) in the Dragonhold patch.
As expected this skill was simply delegated to experienced Dragonknight tanks who could keep up 3 stacks of Stagger easily without much issue.
For the Harrowstorm patch, in an apparent effort to curb usage by tanks, the combat developers added an initial cast time, cost increase by not allowing Mountain's Blessing to affect it and other changes that would make it difficult for Dragonknight tanks to keep up a high uptime compared to before.
Crush the earth beneath you, dealing X Physical Damage to all enemies within 6 meters of you. Debris ripped from the ground is held around you for 10 seconds. Activating the ability again allows you to launch part of the debris at an enemy, dealing X Physical Damage, up to 3 times. The final cast stuns for 2.5 seconds. Each hit applies Stagger, increasing damage taken by 65 per stack for 5 seconds.
This of course, with the help of the Stagger Tracker addon, ultimately did not work leading to Dragonknight tanks still using it and Stamina Dragonknight DPS becoming even more non-existent in any raid composition due to this incredibly unpopular and clunky "DPS spammable" that no endgame PvP'er or PvE'r uses for a damage spec.
How Much DPS Does It Give?
So how much total DPS does (assuming 100% uptime) a Dragonknight applying 3x stacks of Stagger add per person in a raid group?
The answer will lie in the formula below:
[Damage Increase from Stagger = (Normal Hits x 195) + (Crit Hits x (195 x 2.048))]
Stagger affects every class differently dependent on ‘hits per second’, so naturally things like Siphon on a Magicka Necromancer or DoTs on a Magicka Dragonknight will see more benefits with Stagger as opposed to something like a Stamina Nightblade.
Assuming that there are 514 'normal' hits and 558 critical hits on the such as on the Mage Hard Mode fight with 3x Stagger's value of 195, the crit hits on Stagger are multiplied by the average crit damage modifier:
Damage from Stagger = (514* 195) + (558* (195* 2.048))
Which equals to 329,073 Damage
DPS Gain = 329,073/112
End Result of 2.9k DPS Gained per DPS player!
In general, a MINIMUM of 2k DP per person regardless of class is gained from 3x Stagger making it a worthy debuff to have in raids. Basic calculation would be an additional 16k group DPS minimum.