A referrer is the page that a visitor comes from. For example if a user clicks a link on Facebook.com and goes to mybrand.com, through tracking platforms like Google Analytics and similar, you as site owner are able to see the referrer; in this case, facebook.com
Sometimes it can make sense hide the referrer from appearing to the end user. When enabling this option, the destination site's owner cannot typically see the referring domain.
While today most sites inherently use SSL (secure connections) and thus natively hide referrers from passing, some sites do not. When enabled, we use an extra privacy step which strips the referring URL from appearing.
Generally, this option is intended for power users, however enabling this option will not hurt your campaign in any way.