Noted firearms/training guru Massad Ayoob recounted an incident in which a man was forced to defend himself, in public, with his defensive pistol. He prevailed, and immediately after the shooting, he scanned left and right; seeing no further threats, he holstered his weapon. He was then shot, and killed, FROM BEHIND, by his now-deceased opponent's friend. So, the practice of a total 360 scan after firing would certainly seem to have it's merits.
Seen on a bumper sticker: "Exercise. Eat right. Take vitamins. Die anyway."