In short: If I start the game (Windows version) with a USB headset or audio device attached, the game uses that as the output for the game audio. If that device is then disconnected (at any point once logged in - main menu or in game) then the whole thing freezes up, with Windows bringing up a "FINAL FANTASY XIV has stopped working" prompt.
This is a real nuisance as I sometimes watch shows or listen to music with the game audio separated via the main speakers with the volume turned down low. I cannot think of another game I own that has such a problem switching audio outputs to the point of freezing up and crashing like this.
Audio device changes should be a relatively simple problem to sort out but this has been an issue for the whole 3 years the game has been running and should really be fixed by now...