1. Build up a permanent record of every individual on the planet. 2. Sit on it. 3. Wait for an anti-government activist to gain traction in the public eye. 4. Reveal the skeletons in their closet to discredit them.
That and perhaps a secondary goal that is way more sinister. By getting people to realize they are being watched all the time, perceived surveillance, their actions are going to change, complying more towards perceived 'normal' behavior. It will get to self- censorship at its worst.
Straight-up blackmail is not an effective strategy: Hoover failed to blackmail MLK back in the 60's. Their current strategy is to search everything you've done in the past, and find or make up a crime using poorly worded legislation, falsify the investigative trail as to be permissible in court, and threaten you with excessive prosecution, while you rot in pre-trial detention, hopefully milking a plea bargain to serve them political gain or have you turn in your friends. This effectively ends the judicial tradition of presumption of innocence.