The volume control might be disabled in MPD configuration to ensure bit-perfect digital output.
In such a case the volume control does nothing and might be hidden.
Optionally...
Hiding might be possible anyway, even if the MPD configuration allows for controling the volume - in such a case the MPDClient might set 100% volume on startup. The rationale is as above - to ensure bit-perfect output.
The volume control might be disabled in MPD configuration to ensure bit-perfect digital output. In such a case the volume control does nothing and might be hidden.
Optionally... Hiding might be possible anyway, even if the MPD configuration allows for controling the volume - in such a case the MPDClient might set 100% volume on startup. The rationale is as above - to ensure bit-perfect output.