Iconoclast wrote:Also, I see NO reason to always have one instrument at 100%.
You should probably tell that to Nord

This is how most of the default programs are set up. In most (not all) cases, a single piano or organ program has that instrument at 0 dB (100%), and the other programs are then adjusted to suit the same perceived loudness, so the board sounds even across programs.
So it is actually the other way round: There are only a few reasons to go below 0 dB (100%) as the starting point for the individual instruments (but there are some good ones).
Most digital recording systems or modern boards or quality speakers don't need you to hit them with a ton of signal.
That is not what I suggested either, so maybe I should have been less brief. Here's the longer version:
The individual instrument knobs work in the digital domain. The 0 dB level (or 100% instrument gain) means that the output of the instrument is kept as it is generated by the modelling/sampler-playback before being sent to the final output summation and effects. If you reduce it to less (i.e. if you set it to -6 dB) it just means you attenuate the signal a bit internally in the digital domain (which may either discard some of the signal if done in integer arithmetics, or it may entirely keep it almost as if, if the summation stage is done in floating point).
Assuming Nord have designed the instrument well (I think they have), there will be headroom in the digital output chain. Maybe the instruments themselves are based on 24 bit samples and the output summation is done in 32 bits (which adds 48 dB "headroom" if you will). So if you keep the instruments at 0 dB (i.e. 100% on the scale), they will run at their native generated output into the final stages.
It makes sense to me that the overall output of the keyboard is kept consistent across programs, with similar perceived loudness. So the starting point could be that a single acoustic piano or your default organ patch is maintained at 0 dB on the instrument level.
At least, that is how Nord have set up their own programs.
For programs that have more going on, the levels are reduced a bit -- this, I believe, is not to prevent internal distortion, but to keep the levels consistent between programs (if there would be any internal distortion, it would be digital, and it would sound horrible, so not so easy to miss).
So what I do (and I think this is how Nord has been doing it as well) is this:
Single instrument acoustic programs (which I assume are the ones with the lowest perceived loudness) are kept at 0 dB on the instrument level.
When I add more to a program (effects, more instruments, ...) I find a proper balance between the internal voices and then adjust the overall level of ALL instruments so that the perceived output loudness is similar to my other programs. There is even a function on the board to simultaneously adjust all instruments levels up or down, keeping their internal balance
When I play at some venue or at home, I use the master output knob, which I think is primarily working in the analog domain. This one almost NEVER goes to 100%, but I prefer to keep the levels somewhere around 1 o'clock, so that it is easy to make minor adjustments up or down. Usually when the FOH is a 0 input gain (line levels) I end up between 1 and 2 o'clock on that.
Plus: Like Nigel T said, if you're at 10, where can you go?
That quote is relevant in one situation: If you want to adjust one (Nord panel) instrument in a program to become louder compared to the others during a gig, then it makes sense to keep individual headroom in all of those channels. For single instrument programs, just use the master output if needed, so there are hardly any reasons to deviate from 0 dB for those if they match the overall perceived loudness. For multi-instrument programs you will likely anyway be a bit less than 0 dB to match the loudness.
But if you prefer to keep your overall internal digital levels 6 dB lower, feel free to do so! There is -- as you say -- hardly any real loss in a live situation. You may just have to tweak all the default Nord programs you could still be using.