I've lost count of the number of 3D renders I've seen with flat, uniform lighting; where it seems the artist thought that shadows were something to be applied sparingly and subtly, if at all.
Just look around you. Real-world lighting is full of variations of light and shade. Even on the sunniest day, there will be dark corners. The closest you can get to uniform lighting might be outdoors on a completely overcast day. Even indoor lighting is almost never that uniform.
The trouble with uniform lighting is that it makes the picture look like a collage or something photoshopped from pieces laid flat on top of each ot