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.

For example eavesdroppers know who is speaking at the moment among other nasty issues.

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.