Face tracking and eye tracking allows them to determine your point of focus on screen (known as "gaze tracking") as well as how you are reacting to what you're seeing via mood/emotion etc. In the context of the Quest, this gives them a metric of how much you're enjoying certain games, which would allow them to give you more accurate recommendations (ads) for new ones that you might like to buy. Height data can be used to target kids with a very high degree of accuracy, even if they aren't using their own account. It's not about selling these individual pieces of data, it's about more accurately sorting you into the demographics that they allow advertisers to choose from (and potentially open up new ones). Because accuracy sells - if your ad company gets the reputation of being inaccurate, you will lose customers.

It also gives them information on how much you're paying attention to the advertisements you're being shown. One of the big questions in advertising is always "how do consumers respond to our adverts" - how long are they looking at the ad etc. Gaze tracking gives them that information, and has been an area of research in the advertising field for many years. If you're someone who pays more attention to adverts, then you're a more valuable target for advertisers, especially if they are able to make the link between you seeing an advert and a purchase being made. Or if you're someone who doesn't particularly pay attention to static ads, but will pay attention to a video ad, Meta can use that information to tailor what ads you get served. Conversely, if more people than normal are not paying attention to a particular ad, then Meta can more accurately report to the advertiser that their ad is performing poorly, likely far sooner than with other metrics.

So by doing this, Facebook/Meta has improved on two of the core parts of advertising: accuracy and retention. If you are able to boast to advertisers that you can target certain demographics with a higher degree of accuracy, then not only will more advertisers be interested in your services, but you are also able to charge them more money for that luxury. Similarly, being able to boast a higher viewer retention is of great value to advertisers, especially if this can be linked to higher sales, as is more accurate information on how ad campaigns are being recieved.

They state that they use this information for marketing purposes in that same privacy policy. You are definitely getting targeted ads based on it.

You can get a lot more data from a Quest headset than you can from a Facebook account. Some highlights of what's collected according to the Quest's privacy policy:

• Physical details of the user eg height, head and hand dimensions
• Fitness data
• Eye tracking data (not "raw" data - only processed...)
• User facial expressions (again only "processed")
• Environmental information & dimensions (aka. details of the room you use it in)

And it's not about an individual's data being valuable - it's not like Facebook lets you buy access to an individual's data set anyway - it's about what you can do when you have access to millions of individuals' data. Facebook made $113B in advertising income in 2022, or ~$39 per user they have on their platform. Having access to more data like that collected by the Quest means they can more accurately target ads to these users, which of course they can then offer to advertisers for even more money.

What is truth though? You speak of it as if it's an absolute, definable thing, but in reality it's very much not. Truth is a relative term - we can both have truths that are in complete contradiction of each other, even within the realm of modern science.

Let's take a classic physics example - you're on a train, watching the world moving through the window. From your perspective you and the train appear stationary, while the world looks like it's moving beneath you. But from a person on the platform's perspective, they are the ones who are stationary while you and the train are the ones that are moving. If you drop something, from your perspective it moves straight downwards. But from the outsider's perspective, its trajectory is slanted - it's moving forwards as well as downwards.

Which of these perspectives is the "truth"? Is the train stationary, or the planet? Well, both - and simultaneously, neither. There is no absolute, definitive truth of the situation - it depends on whose perspective you take on the matter. And things get more confusing when you add more perspectives into the mix - after all as far as an observer on the moon is concerned, they are the one that is stationary while both the Earth and the train are moving. Or if you were to take the perspective of someone standing at the centre of the universe, then their truth is that everything is moving away from them. As such a definitive "truth" is impossible to define here. You can only state things from a particular perspective or - in physics language - a particular frame of reference.

This is why we don't use the concept of "truth" in science. Because while this is only a single example, this concept extends to basically everything. Science is not the "truth" nor does it ever attempt to be. Science is humanity's understanding of how the universe around us works from our particular perspective. Judging things as absolute truths or falsehoods is antithetical to this concept and therefore to science as a whole.