I never used to use them, but do now. You should see my old Pro Coil when I didn't have a coil cover lol They do the job of adding a bit of protection. I know there is a lot of talk about trapping dirt in the cover and it affecting your machine, but I have not seen much of a difference in true hunting conditions. Some people seal them on, and some people just use car (or truck bed) undercoating on their coil. Some coils don't come with a bottom shell, so you have to use the coil cover. I just use mine without sealing it and clean it rarely lol