[MichaelCrawford]

while strictly speaking, tor does help defend against traffic analysis, that's not its main function.

Traffic analysis is a means of obtaining information from one's opponent without cracking their encryption. It was explained to me by a security consultant, that during a battle you determine where most of the messages are originating from, then drop a bomb on it.

For that reason, to defeat traffic analysis, every node in a communication network sends all the other nodes messages all the time. Even if there is a privileged node you can't tell based on the number of messages it sends.