Read this VERY important interview with two NSA whistleblowers about a program one of them created at the NSA, called ThinThread, that the NSA didn't want to use because it was so efficient and automated that it would eliminate the need for lucrative contracts to be given to government contractors to do the same thing, only more expensively!
But it's much worse than that, because the way the contractors wanted to do the surveillance was by looking at all internet traffic and having people manually looking through it -- a totally absurd idea (you'd need at least millions of people working 24/7 to look through 1 billion+ people's communications) -- whereas the automated system would pick out suspicious activity, then automatically notify humans of legitimate threats so they could investigate further.
Here's the interview: https://opendemocracy.net/wfd/william-binney-mary-fitzgerald-kirk-wiebe/we-could-have-stopped-paris-attacks