Ahhh, rest assured I appreciate your time and realise that it’s often difficult to work out what’s in someone else’s head.
I noticed the “problem” when I first decided to try and apply the new rotation constraints in 2.4.
I tried applying a constraint to one elbow and of course it didn’t do what I expected (in terms of direction) so I turned on Draw Axes and saw the reason- the axis alignment wasn’t “typical”. In the case of this armature, the left and right arm bones (upper and lower) are all over the place. I expect I’ll face the same problem with fingers etc since the axes are inconsistent. I tried rotating a bone around it’s axis but it wouldn’t (I see now that this can be achieved with N-panel, roll angles)
So, I re-read the docs and it stated that the roll angles should be consistently aligned to make the armature usable. It noted that Z-up was usual for horizontal bones, Z-front for vertical bones. It recommended CTRL-N but that didn’t change anything on my rig - that’s when I realised I couldn’t do anything at all with the angles except editing one by one.
I thought it might not matter but I’ve downloaded 3 different armatures in the meantime for various reasons and noted that all of them have consistent Z-up on every horizontal bone. That’s when I figured I was probably going to run into problems if I didn’t sort it out - and since this model was to be made available for general use, it seemed wise to make it “generic” in every sense of the word by making it consistent with othe rmodels.
Plus, it’s frustrating to see that other armatures have exactly the alignments I’m after but can’t achieve.
So, whether z faces forward or upward is probably not a great issue - but having Z point at a variety of angles between the two vertical concerns me immensely - it just looks like potential trouble.