Its only real purpose as far as i know is to keep the valve secure when using it in a rim that has a hole that’s too big. It helps if you’re using a small ‘mini’ pump, because using those is usually pretty stressful on the valve, the way they’re designed. I haven’t used those in many years. Most people don’t need them any more than they need valves that are threaded along the length of the valve shaft, or need the plastic caps.