Talent in Unholy, to restore a rune when a disease is cleansed.
So anytime they cure Frost Fever (your only disease), which is removing the cast-slow or snare, you get a Frost Rune back and can immediately Howling Blast from your spamming of the attack key.
I used to think this talent is good as well. But somehow , no PVP DK is taking this now. I guess people just assume that DK diseases are not to be dispelled.