I never understood this and I don’t think I ever will.
I change the print width of a curve, because there’s no other width quickly accessible:
And then nothing happens in the viewport.
So, I go into the display settings to see if I can change all curves to use the print width instead of the object’s width (whatever that is) and there’s seemingly no option for it:
Why is the UX so crap around this? Why is it so difficult to change the width of a curve?
At one point, I there was a glimmer of a hope of a quick setting, but I don’t think it materialized?