Huh? You're talking about the effect from ring of divine might and heaven's wrath? It is an instant kill on creeps smaller than Catas.
Even McShane didn't know, that this doesn't work on angels? 
And yeah. It is instant kill. Very recognisable when playing with heavy units. When priests have ~1k health and you with heaven's wrath can kill all of them in an instant.
P. S. With heavy units in game settings, this is a very important aspect.