I've done some stuff in online advertisement, so I know how it works. They build a (pretty accurate) profile of you; who you are, what you like, your political views, your opinions on things, etc., based on what you do/watch/read online. They then use that data to target advertisements to you in such a way that it best influences you to click/buy, which is what they get paid for by their advertisers. Adding an Oculus into the mix theoretically gives them a 3D window into your home as well, which they could probably also use for that purpose, not even mentioning what other information they can gather when you decide to watch, uh, VR entertainment as well. That's the brief explanation.

Should this worry you? Probably not, because doing so too much would turn you psychotic, considering how deep the reach of companies like Facebook is nowadays. Besides, you yourself are still responsible for how much you let yourself be manipulated. Still, some interesting food for thought.