Anatomy, of course is essential to any drawing whether it has a direct reference to nature or is completely imaginary. Though a character and/or its action may be greatly exaggerated or caracatured, anatomy in a sense remains fairly constant. An elbow is an elbow and only bends in a certain way, and has its limitation. Liberties may be taken but the "reality" of even a cartoon must be kept or it will lose plausibility or credulity. It is not an easy thing to convert one's knowledge of structural anatomy to the cartoon medium.
It has been said that the location of a joint is more important than the joint itself. For instane if an arm shape has been established, it cannot have an elbow bend in an improbable place, no matter how well the elbow is drawn. Compare tiger's arm to that of a real tiger.