With eye tracking they will be able to determine your interest level to allow additional targeted advertising of things that you eye lingers on. If you saw an alcohol ad and lingered on it because you're a recovering alcoholic they'll know to really ramp up the ads on that since they've identified you as having a weakness to them. Maybe they'll even use iris scans or databases of eye movement patterns to identify you as an individual for even better user tracking.
Funny you say that. Have you noticed how yourube adverts now pause when you scroll into comments?
My YT Vanced recently broke. So I reinstalled stock YT and my god the ads are baaaaaaad. How do people put up with it?
Using newpipe now.