When talking about privacy especially in the context of a social media people often resort to an argument like "What's a big deal, I meant for that picture to be public." and you are absolutely right, that picture of yours is the least important price of information. What's more important is what is called metadata. Metadata that allows provider to answer questions like what he was doing before he posted, what he was doing afterwards, how friends reacted, why he posted and so on and so forth.
Thus protecting your privacy is not necessarily about protecting your data it's about protecting your metadata. It's about depriving providers of those pieces of metadata they would typically use to perfect prediction models they created for you. Models that would better understand you, even better than you understand yourself, up to the point when your next move is sold ahead of you reaching decision point for it.
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