understanding the traffic is often of less importance than knowing who is speaking to whom, or even roughly where they are. Traffic analysis can give law enforcement either valuable leads in an investigation or a nice list of dissenters to harass (depending on your perpsective.) Only problem is: they have to get off their lazy arses and do real investigation instead of just waiting for people to incriminate themselves. They (FBI, CIA) have proven to be fully capable of that kind of investigation on numerous occasions -- how is it that we know so much about the 9/11 bombers if law enforcement can't live without all their new powers?

I don't recall what the date was, but there was a recent New York Times article about how a large number of the al kaida members who were arrested/blown up lately were being tracked by anonymous cell phone SIM's and conversing in an unitelligible manner (long silences, vague references to things like "the big guy", etc.)

Traffic analysis uncovered a network of people around the world who called each other, each could then be tracked and investigated by means of human intelligence vs. purely by means of signals intelligence. Both work, one is just more work than the other.