I apologize if this has been asked before, but after browsing the site I could not find any satisfactory answer.
I recently hit 85 on my Warrior and have decided to turn him into a tank. Now, I understand that Mastery is my most important stat (until full CTC coverage), but exactly why is it so important?
Is it solely based on the fact that Mastery isn't subject to diminishing returns?
it's not subject to diminishing returns, and when you reach CTC with it, it can be effectively treated as permanent mitigation, similar to how we can treat Armor as part of mitigation, and thus, use it for effective health calculations because we know, in the worst case scenario, we'll block, which will be 30% damage reduction. The faster you reach CTC, the faster you increase your EH by a flat 30% (or so)
Welcome to hell (kidding lol) I'm a newer tank as well, (had it down to an art then stopped playing for a while, now back to learning all of the new stuff)
I'm not too technical as most of the people on this site, but basically it "boosts" whatever spec you are. So for a prot warrior (like me) you will increase your critical block. That's it in a nutshell.
There are more informative threads out there, but hope I helped a bit
Even if avoidance did not diminish, mastery (and thus blocking) would be superior in terms of increasing CTC. You work out your CTC by adding your miss chance (5%), your dodge chance, your parry chance and your block chance up together. You reach full CTC against boss level enemies at 102.4%.
When you block, you reduce damage by 30% (or 60% if you critically block). You can therefore imagine your health being 30% higher when all you do is block or avoid melee attacks (not totally accurate but will do for now ).
edit: critical block chance is not added on to your block chance (miss+dodge+parry+block+crit block). It simply chooses whether or not the block will be a normal one (30%) or a big one (60%).
* Once out of leveling greens Mastery provides as much damage reduction as Dodge/Parry Rating, and only increases as you gear up.
* It levels out damage income, making it easier on your healers to keep you alive.
* It's the best way to fill up CTC, which reduces burst damage from bosses as well.
* With the metagem, full CTC (AKA Unhittable) is a guaranteed 31% reduction on all boss swings, which actually increases your EHP by 45%! (Think of it has having a constant baby Shield Wall on you!)