It's not an either/or thing at all. The browsers are slowly trying to tighten policies on Referer, but it's a process because there are still some webpages that unfortunately rely on it being sent. (You can force it off, at least in Firefox, if you want to.) The point of this site header is so that sites that don't need Referer to be set can explicitly tell your browser that, protecting you from snooping third parties.