The ability to speak through different channels using different voice activations.
User X is present in channel 1 which is linked with channel 2.
User X Continuous voice activity is transmitted to channel 2 while pressing the PTT causes all voice activity to be transmitted to both channel 1 and 2.
While user X can hear voice from both channels.
This would be really great in raids in WoW, Quite unsure about other situations where this would be useful.
Another way of doing this which could be simpler, is if talking to each channel has it's own PTT. (Only works in PTT then)
If a user holds "Ctrl + Mouse 3" voice activity is transmitted to channel 1,
While if a user holds "Alt + Mouse 3" voice activity is transmitted to channel 2.