It is always about control, you got it right. I heard a commentator suggest that if Nazi Germany had the ability our government does to spy on it's own citizens, Hitler would have succeeded in killing nearly all those Jews who escaped.
The tools they have have been used for blackmail, case in point General Petraeus. When he balked at playing ball on Benghazi, the Obama administration simply released the emails they had from the beginning to destroy him. Ever wonder what senators, congressmen, supreme court justices, and others have been blackmailed?