Originally Posted by Lycanthrope

Some programs use cookies to track referrals. Many people will in fact signup a day or more later than when you sent them there. Wipe out their cookies and you don't get credit. Webmasters that push these "cleaners" are fucking themselves and everyone else.

Besides, if they are choosing to leave, they obviously do not want to view adult content which means they probably do not have much of any history for them to "clean".