Setting up the the gesture and the proportions help to make drawings more accurate. Solid drawing is also important for accuracy. Next comes value. Here drawing the shadow shapes and filling them in with an even mid tone helps to create depth and volume.
Shadow shapes help to define mass and volume on a figure. It helps to begin with a gesture, then proportion, then put in shadow shapes. In animation and sequential art solid drawing is important so that the viewer recognizes the same character.