The value of my data is not that it can train a statistical model about preferences of developers in their 30s - that's absolutely marginal. My personal data is useful in itself as a proxy for my own life, my preferences, my buying habits, it's a map on how to influence and predict my behavior, possibly against my will.<p>A company having exclusive access to all my personal data, emails, etc. can for example, infer that I have an urgent need to buy an airline ticket to visit my sick father, and extract my reserve price for that ticket, as opposed to an average price for all passengers. Or it can deduce the minimal paycheck I am willing to accept for a job.<p>So even in the unlikely case I can recover the full value of my data from the market, I haven't really earned anything. My information differential is a competitive advantage in the market, and selling it is self defeating, companies are <i>not</i> selling or giving their data back to me. So the more data you sell or give, the larger the asymmetry grows until the only deals you can make are bad deals.<p><i>Edit: I can neither confirm nor deny I am developer and/or in my 30s</i>