I remember just few years ago there was an article here about a website tracking mouse movement to predict what the user will click and pre-loading the content in the background. It was seen as a huge improvement to the experience and the comments section was full of people saying how cool it is. But hey, now facebook is doing it, so it's suddenly the worst thing in the world?
There's a difference between pre-loading content to improve user experience, and tracking mouse movements to gather information about users that's then used to show them advertisements, or potentially track them across the web[0]. There's also the difference between announcing "hey, look at this cool tech we have to make the web faster!" vs "we are legally required to admit that we've been watching you like a hawk, f…
It's a very manual process, but probably one of the most powerful tools for improving user experience I've ever seen. And typically for most businesses, you are keeping these sessions for 2 weeks or thirty days at most.