Besides the fact that you’re much more likely to miss, it guarantees a ricochet every time you miss.
You shoot for the middle of the body mass, to make it more likely you get a hit, and to make it more likely to stop the perp.
I would think that a shot at a slight downward angle would tend to be lethal for a shorter distance beyond the intended point of aim than one which is fired horizontally or upward. A typical self-defense shooting isn't going to allow the shooter much chance to look 100 yards or more behind the target to make sure there aren't any innocents in the line of fire.