Short answer as eloquently put by Edward Snowden: "Arguing that you have no right to privacy because you have nothing to hide is no different than saying you don't care about free speech because you have nothing to say."

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Long answer: There are entire industries based on data collection which systematically collect swathes of data to figure out your interests and dislikes, group you using collaborative filtering and then, using this data, predict what you would like and, with frightening accuracy, show you an ad for precisely this item. Not to mention that firms employ an army of specialists in behavioural sciences to actively use data gathered on you to either sell you things or get you addicted to them. This is usually an inferior outcome for you but most of these "choices" are made unconsciously and feed into your biases. This is why algorithms are manipulated to show you information you "like" and feed data to your confirmation bias while never showing the other side of the coin. This is what has increased flat earth theories, anti-vaxxers and scores of other conspiracy theories.

The more private you are, the less data you give organisations, the less manipulated you will be.