Many people think that having a cover on your air tank is to help encourage ball bounces and to add style points. That is just part of it. Your air tank is an investment and you will eventually have to have it hydrotested. If you have damage to your tank such as dents, scratches, or gouges, your tank can fail when it gets hydrotested and you will have to buy another. A few bucks here can save you money in the future.