The point is ...
1) User visits site via affiliate => gets affiliate cookie
2) User doesn't sign up and closes the browser
3) 3 days later he's horny again, thinks about the site site, type's in
www.domain.com or types your sitename into google
4) Goes to your index.html => tour => biller without affiliate
5) You've a sale that's not credited to the affiliate
If you've multiple tours and billers you usually use a system like NATS that tracks your sales independent of tour/biller.