What pinkunicorn wrote wasn't entirely true. If you are a paying member, the site will run challenge checkers in the background for you. A certain amount is run every day, those closest to you are prioritized. With time, pretty much all challenge checker will be run using your account. Those closest to where you live will be refreshed most often.
The result can then be seen on maps for example, or on the more advanced challenge checker images which has a cross or checkbox to the left.