[bbz]

The good thing about the death bless is that even if you dont kill his army, most of the units that are hit by battle magic(say blade wind) will get afflicions(that is given a high death bless), and thus reducing the quality of the enemy's troops.(imagine half of them having never healing wound -20% hp.).
Or another option hit and run with your mages, casting rain of stones or some other massive battlefiled magic and diseasing 20-30% of your opponents army and then just waithing for them to die.
Another good use is against SC and or thugs since having them get a chest woulnd or become blind is almost equal to destroying them.