There are many situations, think university or corporate networks, where you cannot rely on the IP address for tracking. There are ISPs that don't have enough I

There are many situations, think university or corporate networks, where you cannot rely on the IP address for tracking. There are ISPs that don't have enough IP addresses for users so they many-to-one NAT them and most users won't even notice. Even behind an ISP or corporate NAT with cookies disabled, there are other ways of tracking. If JavaScript is enabled, browser fingerprinting can be very disturbing in its ability to single you out, depending on your configuration. More generally, I always found this obsession with tracking non-users one of the creepier aspects of Facebook when I finally used it circa 2011 - 2012. The amount of information it had about me that could only have come from web browsing before I had signed up, such as local takeaways and restaurants I had used, was impressive but unnerving.