Let's say your wife is looking for a job, but you plan on having kids some time in the future. That data is collected by either facebook, whatsapp, your mobile phone provider or something else. Or her data collecting menstrual calendar isa sending back info (yes this actually exists).

Now, it's illegal to ask that in an inteview, but the boss might buy that data, and your wife will never get a job.

Let's say you are a supporter of a political movement that is not mainstream, all of that data can be used to exclude you from society one small step at a time.