In previous posts I have looked at damage totals from combat logs but this ignores something very important - the heat of the moment, what can happen in just a few seconds of combat. There is one thing I dread to see flash up on my screen and that's a string of big crits hitting me in quick succession.
Looks like this...
When I see just one big number like this I think "oh shit", nevermind three at once. That's over 4000 damage in the blink of an eye. Numbers like this are enough to kill you dead if you are already at low health. When people see you with low HP they go for the kill and you get focused. A string of big crits will either kill you straight off or leave you vunerable and put pressure on healers. Things tend to go awry.
DPS classes are crit-crazy. Go ask one. I believe BWs and Sorcs can get there crit chance up to 75%, other DPS classes to around 50%. They love the stuff.
On top of what your opponent is stacking you also have a base chance to be crit, based primarily on your initiative that has nothing to do with you opponent.
At Level 40 the formula for 'Chance to be Crit' = 35 / Initiative
Initiative @ 100 (35/100) = 35% chance to be crit
Initiative @ 200 (35/200) = 17.5% chance to be crit
Initiative @ 300 (35/300) = 11.6% chance to be crit
Initiative @ 400 (35/400) = 8.75% chance to be crit
Initiative @ 500 (35/500) = 7.0% chance to be crit
Most people's initiative is around 200 so a 17.5% chance to be crit. This means that a Sorc with their own +75% chance to crit will actually have a chance to crit you of 92.5%!! This is scary.
Reducing your base chance to be crit to 0% is not too difficult but what's the point if a Sorc still has a 75% chance to crit you?
It's the chance to not be Crit multiple times in a row that's important. You can survive one big crit. Surviving three is a different story.
Imagine a situation where the DoTs have added up and you have 4000 HP left. A Sorc or two focuses on you with +75% Crit. Added on top of your 17.5% base chance to be crit you will be crit 92.5% of the time.
The probability you will be crit twice in a row is 92.5% x 92.5% = 86%
Thrice in a row = 92.5% x 92.5% x 92.5% = 79%. You will survive 2 out of 10 times.
With a base chance to be crit of 0% you will get crit 75% of the time. The probability you will be crit twice in a row is 75% x 75% = 56%
Thrice in a row 75% 75% x 75% = 42%. You will survive 6 out of 10 times.
By reducing your base chance to be crit from 15% to 0% you are 3 times more likely to survive focus fire. Not only are this but there are lots of nasty procs and debuffs linked to critical hits that you will avoid.
-Crit also obviously gives you a direct overall damage reduction. For most classes a crit is 50% more damage than a non-crit. If a normal attack hits for 400, a crit will hit for 600. Therefore, a 10% reduction in Crit chance = 5% reduction in damage. Sorcs/BW however do 150% damage per crit, so a 400 attack will hit for 1000 when it crits. A 10% reduction in Crit is therefore equivalent to a 15% reduction in damage versus a BW or Sorc. As I have shown in a previous post, playing a SM and being in the front line Sorcs do me a lot of damage.
Getting to 0%
If you look again at the formula and examples above of initiative and base crit chance you'll notice a diminishing return on the stat. Going from 100 initiative to 200 reduces your Crit chance by 17.5% but going from 300 to 400 only reduces it by 3%. I would advise getting to around 250-300 initative and get the rest from -Crit% on items. Most armour sets have a piece that gives -3% Crit so mix and max from different sets you want to use to get the best -Crit.