What is the purpose of using cookies from the referrer in PHP?

When using cookies from the referrer in PHP, the purpose is to track where the user came from before landing on a specific page. This can be useful for tracking marketing campaigns, analyzing traffic sources, and personalizing user experiences based on their referral source.

// Retrieve the referrer URL from the HTTP headers
$referrer = $_SERVER['HTTP_REFERER'];

// Set a cookie with the referrer URL
setcookie('referrer', $referrer, time() + 3600, '/');