kraigwy took my answer. You should be at least functional, if not competent, shooting both left and right handed with any weapons you keep or carry for protection. That includes using any controls, reloading, and, obviously, using the sights and being able to hit your target. You never know when your strong hand might be incapacitated or, as brought up here, you may have to shoot with your off hand to maintain cover or concealment.
"If violent crime is to be curbed, it is only the intended victim who can do it. The felon does not fear the police, and he fears neither judge or jury. Therefore what he must be taught to fear is his victim." - LtCol Jeff Cooper