Painting and making sculpture are today considered as separate pursuits with little interaction between the two. Historically, sculpture and painting had important influences on each other. Below Lorenzo Ghiberti (in his Commentaries) describes some of his contribution to this process:

Also by making sketches in wax and clay for painters, sculptors, and stone carvers and by making designs of many things for painters, I have helped many of them to achieve the greatest honors for their works.

These “sketches” in wax and clay were presumably small figure models. For the painter, they would provide life-like models with the patience of a still-life.
For my current painting projects I have been making figure “sketches” in both clay and wax, and I have been amazed at how helpful these are. Lately I have been using wax more than clay, because wax is more stable than unfired clay. Firing the clay produces a strong model, of course, but it then cannot be changed easily.

[This topic thread moved to The Homunculus]