Shades

In 6th grade I had an art class, I believe, almost every Friday. One class I started to draw the building from outside. Our teacher also had us draw something inside of the building as well. It was a nice day and I remember that the sun shined brightly.
What I would like to point out is how on the outside I could see more easily and quickly the contrast between the light illuminating the building and the shadow cast by the place that the sun was not reaching. Have you ever tried to draw something on a bright day and noticed this? Or have ever just been walking on a summer day and seen the contrast from the shade under the trees and the open areas where there was NO running from the sunlight?
On the inside of the building there were lights and shadows also, but in being outside on a bright day I could really see contrast between shadow and the light compared. Inside where I drew it was much dimmer. I think that is part of the reason that adding shades to a painting or drawing can help make it more realistic. It's a simple thought, but true. In real life there is shadow, and when we draw these small aspects of what we really see into a picture, it can bring that picture to a new dimension. What would the Mona Lisa be without shading? I wonder, if we took shading out of some of the most renowned paintings in the world, would they still have value to us?