The contrast between light and dark is a powerful way to define the focal point in a space. Gestalt theory suggests that the eye is drawn to the places of highest contrast in a work of art because contrast lends emphasis to a subject regardless of the medium chosen.
Value can also give us an illusion of depth. Seeing a gradient from light to dark can remind you of the deepening sea, or the changing a sky during a vibrant sunset.
Value also pertains to colors. In the image above, the dark red at the left of the rose gives a sense of depth, and our gaze naturally scoops across the color gradient, making the rose very
pleasing and interesting to look at.
Lighter colors, like yellow, have more value. Darker colors, like purple, have lower value. The more light, the more value! And of course, the more contrast, the more attention it will receive.
Value is valuable indeed. Whether the contrast will evoke deeply ingrained connotations or give a sense of depth, the use of value will most certainly demand attention.