Understanding how the body works is necessary to recognize the shapes beneath the skin and how the silouete is build. Knowing how to place the bones and the muscles in every pose represent the core of the real understanding of the human shape. Once you understand, you are ready to place the elements, to draw them.
The shape of the bones give us tracks to see how the body joints work. This part of drawing bones represent a deeper study of the human anatomy artwise. Its good to know how the machine works, that help us to understand every bending of the human body.