I don't think it takes a thread derail to answer this briefly. Mumble purportedly can use positional based communications. So if you're to the right of me and you talk, your voice will come out of my right speaker. If you have surround sound, it'll take advantage of that.
That said, I'm not sure that it actually has proximity based communication. In other words, the hope is that if you use mumble and you say something like "Two infantry contacts northwest!" only the people in your immediate area would actually hear you. That way, you're not subjected to tons of superfluous across-the-map chatter. But that's not how I understand it works. Someone correct me if I'm wrong.
The other issue is adoption of mumble.