If we set the world unit to meters then the default grid is 18x18 meters, which is a reasonable working area for cars, house, etc.
If I set the world units to millimeters, then I will be presumably be working on something small, so my grid region should be roughly on THAT scale. I"m not going to build a house in millimeters!
However, the 3D view grid does not scale in parallel with the world units. That means if I set world units to mm I am left with building a tiny object smaller than one grid spacing!
If this makes sense for Blender projects, the grid scaling should match the world units automatically.
(for some reason the world unit scale data path is not available so I could not make a driver for myself)
There is also the issue that for a long time now the units in blender in different places do not respect any global scaling factor. For instance, the properties panel in 3D view provides a checkbox for Edge Length in Mesh Display. The display values do respect either the grid scaling OR the world units. All kinds of Addons have the same problem. It would be nice to see a refactor to fix all of this.
Waddyathink?
