I want to weigh in on this subject because the unit system (which was updated not that long ago) is to me un-intuitive and inconsistent with other CAD and worst of all, messes with the accuracy. It also just makes no sense the way it operates now.
I know this is not an issue for landscapers and sculptors, and probably architects, they probably don’t even really think much in units (maybe meters or kilometers, which is easy to convert in your head).
But for the rest of us who do all of the oddball stuff, we may heavily depend on units. I can’t convert 3.85 inches into mm in my head so I need Blender to manage those issues for me.
Here is the biggest (real, not opinion) issue: If I make an extreme unit, say a ‘micron’, or a millionth of a meter, all the math in Blender works at that level, with all of the limited resolution and accuracy issues. You might say the stage stays the same size but your actor is now microscopic. None of the stuff on a regular stage (cameras, lights, microphones) will work on an ant.
Have you tried to do a ‘keypad .’ zoom on a part that small? It doesn’t work. And the viewport camera range gets unmanageable.
Also try to define a ‘light-year’ unit, say making a realistic model of a galaxy. It’s impossible. You just have to model in ‘Blender’ units and mentally label them ‘Light-year’ units.
So, just like Turntable vs Trackball arguments, I see two fundamental opinions about what units are good for:
A) Changing the scale…all calculations are performed as blender units but REPORTED as a different unit. So when I change units from inches to mm, a one inch tall object will then be described as 1mm tall. This has no calculation issues at all and can use literally any scale of units desired.
B) Converting the units…the one inch tall object should be 25.4mm if I change from inches to mm. This also has no calculation issues, unless you like to design planets in mm. I do this all the time depending on where my numbers are coming from (switching units, not designing planets in mm).
The problem is that Blender is mixing the two! And that causes the problems mentioned above.
(not to mention that the grid has its own scale knob independent of the unit system)
We need a global scale knob (for case A) and a working units knob (for case B).
And yes, I frequently model stuff that needs real units to manage a large range of scales (sandbox environments). YMMV.