Leaks information about the voice stream. It's not inconceivable that a well trained algorithm could recover sentences from the transmission pattern, although I don't know for sure if it could do quite that well.
If they actually cared about offering a secure product that would be enough all on its own.
Compare over in the SSH discussion IdentitiesOnly a feature that avoids the relatively smaller leak of potentially allowing an adversary to correlate your identity if you voluntarily connect to their server.