Mumble was designed as a low-latency, high-quality voice communication for gamers. Mumble includes game linking, so voice from other players comes from the direction of their characters, and has echo cancellation so the sound from your loudspeakers wont be audible to other players.
Your position ingame is transmitted along with every audio packet, and it uses standard DirectSound 3D to position the audio on the receiver side. Only games for which a plug-in has been written get positional audio. All other games will work as well, you just will not get 3D sound.
If you change your audio environment suddenly and drastically, by for example disconnecting and reconnecting your microphone or dragging a piece of paper directly over the microphone, you will throw the voice preprocessor off balance. It will recover, but it will take time.