Maybe this is old news for some people, but if you haven't noticed, concussion blow has not been triggering the GCD (since 3.0.8). You can't use it when the GCD is ticking, but you can stick it right in front of another ability.
What does this mean? Well, there is even less of a reason to not be using it -all the time- when tanking, bosses in particular.
Three decent places to put it for boss fights - one would be in front of / along side Shockwave, a big satisfying smash of damage for bosses - this is also the least efficient way of doing it, however, since waiting for Conc Blow's CD to always come up means wasting 10 sec of Shockwave cooldown.
Another is in with your (shift-modified) revenge, which is probably in a good spot already for you, and your sure your going to be all over that button every 20 seconds. You may miss the CD by a few seconds if your S&B proc delays using revenge every five seconds, but its pretty close.
And finally, doing it manually. My only beef against this, is that its an extra key press that has to be post GCD, but before your next GCD activating ability.
I plan on further testing all the options, but I'd be curious to hear if people have been using it in any of these fashions, and which they find most helpful.
F2P and Conversation
10 hours ago