Josh Burton points out these excellent notes taken from John Lasseter’s presentation at SIGGRAPH 94.

One of the biggest differences between hand-drawn animation and computer animation is the fact that computer animation is truly three dimensional. The first run cycle I ever animated on the computer looked great from the side view, but when I looked at it from the front, the arms were going through the body and the knees were bending the wrong way. From then on I always animated with two views of my character always showing, so that I could always tell if the animation was working from all sides.

Great find Josh!