Added bonus: these extra pre-loads on hover will tell you if someone nearly clicked a link. Your web server logs contain some poor-man's eye tracking. Could aid determining if important parts of your pages (warning messages and so forth) gather enough attention.
Seems like an invasion of privacy. I'd be surprised if someone hadn't used this sort of script for this already. Perhaps browsers or ad blockers will block this feature in the future.
There's already other libraries out there like Fullstory, which tracks all the user mouse movements and interactions with the page and allows you to watch a user interact with your site in nearly realtime.
There are full tracking tools that do a lot more than this already - tracking all mouse movements and key presses. They are often used with the knowledge of users when testing UI changes/experiments, I've even heard of more general versions running as a browser plug-in for medical monitoring (watching for changes in coordination of people with degenerative conditions, without it feeling like an active test accidentally biasing results), though I would also be surprised not to find the idea already used more widely (and perhaps more nefariously) without users knowing.