Is it needful? Unless you are perfect and live in a perfect world, yes, your defensive plans should include methods for coping with injuries.
Not all injuries happen during the deadly force event, either.
During this past year, three of my friends have gotten injuries that kept them from shooting with a "normal, two-hand hold." One friend has a torn rotator cuff in his right shoulder - he's looking at probable surgery followed by six months of rehab, with no right-handed shooting during that time and limited use of his arm for the foreseeable future. Another friend was in an accident and damaged both her wrists, leading to multiple surgeries and extended rehab. Of course at first she could shoot with neither hand, but because the surgeries were more than six months apart, as she began the healing process there came a point where she was able to shoot with one hand only. Another of my friends endoed an ATV early this summer, shattering his arm.
Should these folks all forego carrying a defensive handgun? I don't think so, and neither did they. They're all wearing casts and slings and braces and such, and as such, look like easy prey right now. And they all need to continue their normal lives, going places just like they did before they got injured.
Should they carry defensive handguns they don't know how to use safely or efficiently? Silly question.
Fortunately, all three already knew how to shoot. Two of them were well-practiced in one handed firearms skills, and so took only a single afternoon after their injuries to reassess their newly-limited capabilities and decide how to proceed. The third ... well, the third could already shoot one handed, but had a heckuva time learning the one handed load/unload/reload/malf clearance sequences. Managed it in the end but the journey wasn't fun; it is difficult to learn new material when you're in pain, after all.
How often does such stuff need to be practiced? That depends. For me, I practice a little one-hand-only material every time I go out, just as part of the routine. The basic one-handed gun manipulation skills (drawing, loading, unloading, reloading, malf clearances) I practice two or three times a year, simply to refresh my memory about how to do them safely and efficiently.
I would NOT recommend practicing one-handed gun manipulations unless and until you have had someone show you how to perform them safely, and have that person watch over you for safety while you learned how to do them with an empty gun.
Will learning one-handed skills damage your ability to shoot two-handed, or develop bad habits? Nope, quite the opposite. Once I got serious about learning to shoot well with either hand, I found that the effort of schooling my left trigger finger to be as accomplished as my right one actually taught me a lot about the skill itself. I became a better right-handed shooter as a result of learning to shoot left-handed.
Remember, the basics of good shooting are always the same. No matter what you are doing, the gun must be aligned on target at the moment the hammer falls, or you won't hit. The specific stance is a variable but the related constant is that you always need to provide a solid platform which allows you to have the gun aligned on target at the moment the hammer falls. A smooth trigger press means you don't jerk the gun out of alignment at the moment the hammer falls. Whenever you practice shooting, whether you are shooting conventionally or non-conventionally, you must achieve these basics. Getting better in these basics non-conventionally means that you will have a more solidly-grounded understanding of where your personal limits are and what you must do in order to achieve your hits, no matter how your body is positioned while shooting.
To sum up: yep, you need to learn this stuff. Nope, it won't damage your current level of shooting ability. Have someone show you how to do it safely, and practice it often enough that you'll remember how to do it even if you're in pain from a newly-set broken arm.
pax
