Cookies and how it affect

This is a question you could have looked up on the internet. http://en.wikipedia.org/wiki/HTTP_cookie Referral links sometimes make the site store cookies on your computer so that when you close the site and come back later the user behind the referral link is still credited; removing the cookie and then registering will cause the user to be not credited. Other sites require immediate registration after visiting the referral link and thus not storing a cookie through which the user is credited. Other than that nothing happens. You won't lose users and other users won't lose you.

I think they're used for authentication and storage. When I say storage I believe it's more on site preference and identifiers. I just don't know if they're used for referral links. You can research more though since I think you know more about internet than I do hehe. :D