There is a reason why nude figure studies were undertaken by artists during the Renaissance period as evidenced by sketches left behind by famous figures of this era. In fact, this practice dates back all the way to the Archaic period (7th to 5th century BC) and is still relevant today.
Drawing nude figures enables the artist to gain an understanding of the human form through a variety of body types. Viewing different poses and angles of the skeletal and muscular landmarks of human anatomy allows for deeper examination and understanding of proportions, perspective, lighting, and shadows.
While it is possible to learn from a figure clothed in leotards or tights, studying a nude model is more effective for directly analyzing surface anatomical landmarks without being obscured by clothing or drapery. Incidentally, artists study drapery and the draped figure as a separate subject which in itself is a pursuit that requires many hours to master.
Visualizing the human form beneath the clothes is an approach adapted in various mediums. For example, character design and 3D character modelling often begins with the creation of a nude base figure before costumes are added on. Studying the nude model has greatly benefited students and continues to be a core element in our curriculum.