Det improves, your Auto attack potency and some skill damage, but i heard that before 3.0 it was nerfed or at 3.0.

As far as that goes tho its still not a bad idea to stack it if you can get it.

As Far as stats go however, Play to your style. For me i play a heavy crit based DRK and focus on alot of crit and skill speed i think like most of the game to improve my overall dps.