More than any other tank, Paladins look favorably on Blocks. However, blocks unlike dodges or parries is a mitigation mechanic. Even if you block something, you can actually still take damage from it (that's why a lot of Strength is a good thing). It takes 16.29 Block Rating to grant a 1% chance to block, making it easier to gear for than either Dodge or Parry. Furthermore, blocks tie in with important Protection talents such as Holy Shield, Redoubt, and to a small degree even Reckoning if you're so inclined to pick up the talent. Block Rating is cheap and good, and at many points during an encounter, such as when Redoubt procs, you'll find yourself blocking pretty much every darned thing.
Not to be confused with Block Rating which improves your chance to block, Block Value determines how much you block. Each point of Block Value absorbs one extra point of damage. While Warrior tanks also depend on shields, Paladins make special use of them with Shield of Righteousness, which bases its damage off a shield's Block Value. For Paladin tanks, Block Value isn't just mitigation, it also means more damage and consequently more threat. It's important to point out that blocking is calculated after all other forms of mitigation (such as armor) is factored in.
Understanding the Hit Table
Unlike other class archetypes, tanks must be familiar with the all-important Hit Table. It is critical to understanding how tanking works and it guides gear choices. Similar to pen and paper RPGs, a raid boss makes a single attack d100 roll to determine the outcome of a strike on a tank. This attack roll works off a linear progression of possible outcomes, which go something like this: Miss > Parry > Dodge > Block > Hit > and Crit.
Defense works to increase the values of the first four possible outcomes and -- when capped -- pushes Critical Strikes off the table. Let's assume that a tank has enough Defense to eliminate Critical Strikes, has taken the appropriate talents, and has a passable shield with a 10% chance on Misses, Parries, Dodges, and Blocks. The Hit Table will look something like this:
ROLL : RESULT
01 - 10: Miss
11 - 20: Parry
21 - 30: Dodge
31 - 40: Block
41 -100: Hit
- : Crit has been pushed off the table
So if, for example, the raid boss (aka Blizzard's servers) rolls a 6, it'll miss. If it rolls a 14, you will parry its attacks. So on and so forth. Those values will vary depending on your actual scores, but will always push the table downwards so in theory a tank with phenomenal ability scores and combat ratings won't ever get hit. This can actually happen with Paladin tanks when Holy Shield is active and Redoubt procs, which is an additional 60% in addition to the Paladin's base chance to block. With enough percentage to be missed, to parry, and to dodge, a Paladin can sometimes block all incoming attacks (that don't miss, or are parried and dodged, of course).
Obviously, the best would probably be a crazy chance to be missed by the boss, which pushes everything down. But Miss, Parry, and Dodge all contribute to moving more Hits off the table so the more of the defensive stats you have, the less chances you'll get Hit. The Paladin tank can fill everything in between with Blocks.
Wrapping up for now
Whew. That's all we have time for today, but I'll pick up on the next installment sooner rather than later because there's just a whole lot we still have to talk about. Tanking is about the most technical play style in the game, more so than healing or DPS. This is because there's much more to learn. Today we just went over survivability mechanics but there's still a lot to look at -- from threat generation, talent builds, and common rotations. Tanking is challenging and utterly fun. When dual specs roll around in Patch 3.1, I'm hoping we'll see a lot more players take up their shields and lead the charge.