While working on obtaining my basic peace officer certification, an officer with the Rome City Police came in to talk to us. This gentleman was very nice, but he was missing his right thumb(I believe he was left handed). He was missing his thumb because, according to him, he shot it off while using his non-weapon hand holding the retention flap open on his duty holster.
It is always good for people to learn how to properly holster their firearm. Most people might believe this to be a non-issue, but there are some people who do not properly holster their firearm.
I have seen officer slowly pull their firearm, then holster as fast as possible. The fact is that that is the total opposite to what they should be doing. During those times that a firearm must be drawn, then it should be drawn as fast as possible, then holster the weapon only after the aggressor(s) are neutralized, then slowly holster the firearm, while assessing and possible secondary threats, and only holster it with one hand.
At least, that is how I was trained down at GPSTC(Georgia Public Safety Training Center, aka. "GipStick) during Judgmental Pistol Shooting/Training, or Judgmental Use of Deadly Force(Ability, Opportunity, and Jeopardy!).