If enabled in settings, during multiplayer games players will be able to talk in voice. It will be either always-on or integrated with diplomacy (i.e. voice will work while diplomacy window is open to another player), or maybe voice channels will be always-on but only for those with Pac...
This would be a real bummer, as I thought this exact setting is basically giving me a playback speed improvement similar seen in VLC and mpv player under ubuntu with my eGPU setup (from having 100% CPU usage and still lagy video playback to almost no CPU utilisation and a flawless video...