Hammers are great for putting up pictures or nailing a board over a window. But if you have a project that requires hundreds of nails, using a hammer will wear you out in a hurry. A nail gun is a powerful tool that will save you time and a lot of bruised fingernails. Just imagine being able to drive a nail in one click of a button rather than four (or more) swings of a hammer. Most nail guns are pneumatic, which means they require a separate air compressor to operate. If you don't want to make the investment, you can usually rent both machines at your local hardware store.