Imagine if someone like Hitler came to power again and decided to exterminate people of certain ethnicity or political interests. He or she could just order or seize a data dump from all those companies and have everyone ready to be rounded up. During the WWII Germans would seize church records and censuses from government buildings to easily find people to arrest and dispose of.
Today he or she would have an app for that...
I think just as likely, governments use this information to try to elicit responses to various stimuli. They treat voters as consumers and consumers as animals that they can train to react via various kinds of repetition and rewards. More granular data allows them to be more precise in these marketing and behavioral manipulation methods.
