Just something they teach you in a beginners course because they have to, isn’t it? Nobody else bothers, so why should I?
Actually, warming up is important. Everybody should do it every time. Make it a habit before you shoot, and it is easy. It is often said that it reduces the risk of injury. The evidence is actually a bit mixed on that one, but on balance it seems sensible. Warming up does literally warm up the muscles, and warm muscles work more efficiently, there’s no doubt about that. Why handicap yourself by not doing it?
DON’T STRETCH! How many people do you see do a cursory pull of the elbow round with the other hand a couple of times before shooting? I know a lot of people were taught to do that, but please don’t, it isn’t good for you. Stretching before physical activity can actually make you perform worse.
Don’t get me wrong, stretching is good. Those of us over 40 in particular benefit as the range of movement in your joints tends to reduce as you get older, if you do nothing about it. A regular stretching routine can help keep you supple, but do it after you shoot, not before.
I’m not going to go into details of the specific exercises – there are lots you can do, so ask your coach or look it up. Spend a good five minutes on it, concentrating on the upper body but doing something for the whole body. Your whole body is involved in shooting, after all. Warming up should be gentle repeated movements to get things moving, gradually increasing in intensity, but always staying within your normal comfortable range of movement.