I often use one of my Pose-able Mannequins to figure out how to draw a limb in a believable way, or to show how a shadow would fall near a figure.
Years ago, I was so lucky to be given 2 Art S. Buck Anatomical Manikins as gifts (thank you, Chuck) and had no idea how expensive they have become. A single figure is $80 on Amazon.ca.
They are REALLY great, but honestly I can get the same mobility and variety of poses with an Action Figure that I bought at the Salvation Army for $2.00!!!!!! Who knew?