Short description of error
There are a few problems I kept encountering when trying out the "Bake from Multires" in both the old Blender Internal and Cycles.
These problems are still visible even now, for example when I bake a Displament map from the Multires modifier.
(Original Multires Sculpt)
The result never really matches the original in multiple ways.
I experimented further with a couple of simple strokes on a cube with Multires Level 6.
But once I baked a 16 bit displacement map from multires onto the level 1 subdivision of the same cube
and used that texture via the displacement node in the material, it looks like this.
I used both displacement and bump for this picture.
The big negative point is that the overall displacement never matches the original mesh, regardless of how I set the midlevel and scale settings in the materials or even the displacement modifier.
When looking just at the displacement we can see that on the 12 edges of the cube mesh the displacement breaks.
And when just using the texture via the bump node for the normals, the baked high-res geometry is clearly visible as if set to "shade flat".
Here is the .blend file I used for the cube example.
There might also be some settings that I missed but at this point I really don't know anymore.