I have encountered this weird issue: When not using a BDSF in Cycles, the shadows of my mesh are not rendered properly. How can I have my mesh have uniform color, without any variations in shading, only the shadows? When I connect the RGB socket to the material output, the shadows disappear. Is this a bug, or am I missing something? IMO, the mesh should still cast shadows as Cycles is a path tracer, and some paths would necessarily get blocked by the mesh geometry.
This should be easy to replicate - Blender 2.93 with standard settings. I have changed nothing other than setting the renderer to Cycles and subdivided and extruded the plane a few times.