Many people service their computers without using an anti-static mat. Usually this doesn't cause a problem. However, it takes only one spark of static electricity to destroy an entire computer. It is wiser to take precautions against this possibility.

The green & yellow cable (right) will be clipped to the central heating radiator, which is well grounded through the plumbing. Components that have been removed from the computer and are being handled should be grounded with the black clip. The blue stretchy cable goes to the wrist connector.