Found this story fascinating and scary at the same time:

https://www.guardian.co.uk/technology/2013/jun/21/nsa-surveillance-metadata-content-obama

Among other things, it links to this page on a German politician who sued to have his records released to him.  He handed it over to a newspaper who put together a reconstruction of his life using this “harmless” metadata.

https://www.zeit.de/datenschutz/malte-spitz-data-retention

Pretty scary, huh?