@nektarios said:
... the impression he or she will get is "Oh, let me click this to get a natural sound, natural balance).
That impression would be correct, assuming "natural" means the resultant air-pressure waves would be objectively the same as the air-pressure waves generated by a live performance in the real physical world.
If you confuse -- as Kenneth does -- "natural" to mean "artistically preferable", of course there's no button that can read the minds of your listeners to find what they prefer to hear.
What natural volume is to me is this for example: I go to some hall and there is an ensemble there but there are no microphones whatsoever. The sound coming out of this ensemble is natural (irregardles if it's pleasant or not). Like this one: https://dl.dropboxusercontent.com/u/33556625/Music/Chamber%20Orchestra%203.m4a
Just my iPhone recording. There are no mics, just the natural sound of the instruments and hence volume. So I expect that is what natural volume tries to simulate.
If you set your volume faders all to the the same level, turn on Natural Volume, and use only velocity (and instrument-positioning in the MIR room) to control loudness, your will get combinations of timbres limited to the combinations which are possible in the real world. This optional limitation is the purpose of Natural Volume. When you want real-world-possible timbre-combinations, allign your faders, turn on Natural Volume, adjust velocity (and instrument-positioning in the MIR room) to countrol loudness, and leave the faders alone.
When you reduce velocity on your drum to 60, you are taking advantage of Natural Volume. When you alternatively leave velocity at 100 but attenuate by 8 db, you're breaking the don't-touch-your-faders rule and you end up with a combination of timbres which isn't possible in the real world. In the real world, you can tell the drummer to hit the drum less hard. That's like reducing velocity to 60. In the real world, you can't tell the drummer to hit the drum 8 db quieter while maintaining a constant timbre. That's physically impossible in the natural world; that's what you get when you leave velocity at 100 but lower the fader 8db.
None of this is to say what your listeners want to hear, or how you should do things. Just describing the objective science of the Natural-Volume button.