Cellular companies use it to detect fraud by flagging unusual call patterns. Banks analyze electronic payments to detect buying patterns. Intrusion detection systems do it to signal unusual packets. Of course, there will be a lot of false positives. By itself, traffic analysis cannot tell us more, but that's not its job.
Traffic analysis is a statistical tool and thus requires large amounts of data.
It also requires the computing and logistical means to gather it, including access to points where traffic is concentrated. But once a single entity in a big set is singled out, it is no longer an undifferentiated contributor to the overall traffic. It acquires an identity in the eye of the attacker, and from here other techniques can be used. But this is where the scope of the article ends. Perhaps with the ding of a bell.