Beating him to it here, but firing a warning shot, using a low power first round, or aiming for a lesser injury is a dangerous prospect. In doing so, you are making a statement that you did not feel you were in mortal danger when you pulled the trigger. This may show a jury that you were intending to intimidate someone rather than protect yourself.

If you have a gun, and the person does not respond to the visual deterrent or verbal warning, You are in mortal danger. Once they run away, you cannot shoot them either.

As for low power loads, a .22 can be lethal. Ask any cop in a city with gangs. (Not that I would ever use a 22 as a PDW) Bird shot will blow through a door, what do you think that would do to a face? You want non-lethal, use a cricket bat, or pepper spray.