"Does your drawing have weight, depth and balance?" Basic principle of three-dimensional drawing. What does that mean exactly? It's the art of creating an illusion of depth.
Animation maquettes are used by animators as a three-dimensional "model sheet" to help the artist stay on model and with the visualization of the character. A feat less daunting for animation that is being done digitally.
Animator Marc Davis sculpted perhaps on of the first maquettes for Snow White and the Seven Dwarfs.
Whether it's CG or hand-drawn art, artist have the desire to get their hands "around the model" from every aspect, whether that be literal or implied.
Kent Melton is a sculptor who did absolutely amazing sculptures for Disney's Treasure Planet. The rolling, heavy masses and volume of Glen Keane's John Silver and the almost fragile S-curves of Ken Duncan's Captain Amelia were reproduced flawlessly by Melton in three-dimensional forms.
Artists aim for truth in their work ultimately. Sculpture is tangible almost literal way to capture the truth about a subject. The concept of "sculpture" needn't be limited to clay or tangible materials. It is a concept that should be ever present in the work... especially if it's being hand-drawn on paper.