Interesting topic, b/4 I ever shot IPSC or later IDPA I spent forever shooting Bullseye, the one hand gun, and the off hand in the pants pocket.
ISU was a gun at 45 degrees start, slow fire, timed, and rapid fire.
When shooting either of the action sports, there were times when the the target(s) could be shot with less strain to the upper body, if they were engaged one handed, low and behold, most likely because of my years of one hand shooting, I noticed I was real quick, and accurate. In fact it is way easier to swing side to side with one hand than two.
IMHO this is a good skill to cultivate for "Real world encounters" as sometimes the off hand is otherwise engaged. Just my 2c.