If there is too much static electricity hanging around, it can actually disrupt your computer, causing the screen to freeze or creating various other unpleasant disturbances that can destroy data. Static can even destroy the circuits inside your computer. Extra static can develop from the weather or from certain kinds of clothing or from activities like petting your cat while working on your computer, shuffling around on the carpet, or rubbing a balloon on your head. So a variety of antistatic devices have been developed to help prevent this, devices such as wrist bands, floor mats, sprays, and little metal pads that say "Touch Me."
It's particularly important to discharge any static on your own body when you open your computer to install another card or perhaps a SIMM or two. You don't need a special antistatic device to do this-just touch something metallic before you handle the circuits. Most computers have a metal plate inside the box that's perfect for this purpose.