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Indeed it's totally worthless data, like what are you going to do, dissect people into groups that you could heavily target and try to sell them gizmos or swing an election? Pfft, not worth the effort. There are no companies or state actors are into that kind of thing.

Individual data is useless, but big data is worth gold. It can show you exactly where your target audiance is, and what they're common interests are. That's super valuable information if you want to start ad campaigns.

It has worth, only not the way you mean. It may (or may not) lead to better sales through ads, but it leads to more and more expensive ad sales and some very wealthy companies.