Do you waste time online, surfing through meaningless blogs dealing with technology, mountain biking, etc?
You can even categorize sites. For example, if some sites are simply time killers, maybe while you are procrastinating doing more important things, you can specifically monitor your time on those sites. You can give them all a label: Procrastination, and then see how much time you have procrastinated on the web!
This is one of those goodies that would not have much purpose to most people, but it could be useful. If the computer was a company computer, the usage could be tracked. Or maybe a person setting a goal to do two hours of studying a day, could check how much time they spend on more studious sites (i.e. Wikipedia).