I think this is one of the fundamental misunderstandings: Metadata includes such interesting things as "who has been sending messages to whom at what time" and potentially also from where (ip address). This is an avenue to reconstruct social networks and behavioral patterns, especially if you can crosslink the data with other public sources. I recommend this visualization of the movement profile only derived from the collected data of one german politician (sorry, german only but fairly easy to understand) http://www.zeit.de/datenschutz/malte-spitz-vorratsdaten
