First off, I’m not convinced they are just collecting metadata and not actual content of communications. But in any event, I’ve never heard whether whatever data they are collecting is stored and archived in a searchable format. If so then it is chillingly intrusive.
What's all this NSA data collection about?
It's about using the collected metadata to build social networks.
The NSA has been creating maps of American citizens' social networks
Why do they want to do that? What could social networks be used for in the hands of government? Consider:
Using Metadata to Find Paul Revere
How will such capabilities be used now? How They Hunt
Is it already too late?