I'm testing aggressive block atm, I'm not too sure if I am missing an underlying mechanic behind it but as of now:
-Yes, it hits for a pathetic amount of damage bur raises base block by 10%. Against any other melee class this leads to more retaliation (which hits hard as hell) and more damage. Puzzlebox is right on it not doing much vs. a mage, who has no physical attacks to block with.
-In a 1v1 scenario vs. a mage, I can see omitting aggressive block and not wasting a GCD every 15 seconds on a minimal damage attack, but in most WFs you are taking damage from multiple sources and MMs, which you can block, since much of their damage is physical and weapon damage. If you really wanted to optimize vs just a mage, sure you could take it out or use it manually.
In the chaos of a WF, when a MM or rogue can pop out at any time and hit you with blockable damage, I don't see anything wrong with a GCD being sacced every 15s for 10% extra block at all times.