There has always been a strong suspicion of what was happening (as far as post 9/11 stuff), but no solid proof in the public realm. We learned a little bit in 2005 from Mark Klein exposing the AT&T wiretapping. In 2012, 3 NSA whistleblowers came forward to confirm the AT&T involvement.

Snowden has gone forward with providing more evidence to show what is going on, with enough depth to reveal the full program name and reaches. It's the difference between having hearsay vs real evidence. Very useful for establishing standing for legal cases to proceed. And a number of them have begun to be filed and given the goahead from judges to proceed.