It's been interesting to see some posters refer to this topic in the context of a beating, or a "pistol whipping", a "face slap", etc., what is sometimes required is a move that regains the element of surprise. A boxer uses the left jab in order to set up the right, a strike with the muzzle can have the effect of repelling an unwanted advance, moving the individual out of your line, or as stated before, regaining "tactical" ground or the surprise factor. A situation that turns from lethal force required to less than lethal force required seems to me an example of when such a strike might gain either time or distance needed to extricate one from danger.