Requests made from a document, and for navigations away from that document are associated with a referer header. While the header can be suppressed for links with the noreferrer link type, authors might wish to control the referer header more directly for a number of reasons:

For a long time, I’ve argued that the debate about privacy isn’t about privacy per se, but that it’s really about control. The first step is making people feel comfortable that they are in control of their data. The second step is building tools to help them monetize their own data.