It allows you to see the range of brightness and contrast as the photographer/designer recommended. The problem is, the bulk of crap tossed on the web is not calibrated so you’ll only really benefit from looking at semi-pro/pro photographs and designs. Still a good thing. If exact colors and brightness/contrast are important to you, invest in a colorimeter. The Pantone Huey is a nice unit, at the end of the test they show you before and after which is usually a shock as the difference is quite noticeable on most monitors.