GRANDNESS - In the above photo, the shadow cast by the trees add depth and interest to the photo. While the one tree is the main focus of the image, the shadow produces texture to the image as well as acting as a point of reference to show the scale of the tree.
DIRECTION - In this image, the shadow is playful, used as a curvature that the viewer's eye is drawn to and then follows around the main point of interest in the photo, the flower garden. It is similar (but more subtle) than using arrows to point out the flowers.
MOOD - The trees break up the vast lawn on this golf course. I think the shadow casts a graceful and almost lazy shadow, almost as if the trees were sleeping. The peacefulness of the surroundings, the lack of carts, roads or people shines through.
Here is another example of a shadow directing the viewer's eye to the main part of the image - in this case the garden bench. This is an effective way of featuring the bench, but more importantly, the perennial border behind the bench. Because the shadow runs parallel to the garden, it acts like a frame...
Interesting how in all the images, the shadow was not the purpose of the photograph, but played an important part in the photo. The shadow is the "supporting actor" to the "star" of the photo.