Texture moves the eye. Shadows, monochromatic shades of the same color, create soft patterns to capture our attention. Understanding texture can add dimensions to our projects as we learn to layer visual textures (instead of solids) for greater depth in our designs.
Monochromatic compositions need not be static. For example these photos of
Summer Phlox ("David") flowers and the bark of an American Sycamore (Buttonwood) sapling. Okay, the flowers have some contrast with little bits of dark background, and the bark has a few drops of a greenish lichen diluting the grey-browns. But you get the idea.