[Nextgrid]

You are extremely naive if you believe Google can't infer anything if the referer is missing.

An IP + user-agent combination (both of which are sent) is enough to uniquely identify a typical home user with high certainty unless they're behind a carrier-grade NAT and use a very popular browser.

[dlubarov]

Let's assume Google can identify the user but doesn't get a referrer. So what? The only information Google receives is that some user visited some unknown website at a particular time. How exactly would that lead to Google increasing its profits?

[Jensson]

They know users activity hours better that way. At scale that is valuable data.

[codethief]

But that's still not personal data.