as a monitor is on for a while it will build up a static charge.... this charge can distort the color and shap of things on the screen.

most people that have problems with it have big (read: 19inch+) monitors and are doing graphics work or something that requires them to have a crisp clean picture.

Better monitors have methods in place to prevent it in the first place and therefore don't come with a degauss feature.... that or really cheap monitors