One of the major advances in the last decade or so in intelligence gathering has been social-network/cohort analysis. Phone metadata makes it possible to identi

One of the major advances in the last decade or so in intelligence gathering has been social-network/cohort analysis. Phone metadata makes it possible to identify relationships between people. Let's say you know two "terrorists". If you can identify, say, 3 other people who are all friends with those two then you can tentatively identify those folks as possible terrorists. If you obtain other information such as actual phone conversations, email, etc. then you might be able to confirm that, which then gives you the ability to find their friends, and so forth. Potentially it's an effective way to identify folks who might deserve more investigation. Though it's highly questionable how effective it is as a means of stopping crime or terrorist attacks.