Originally Posted by Joe Perez

The one thing I can't easily do with a pencil and paper is visualize how parts interact in three dimensions. Say I have a box, and I want to pass a tube through it at a weird angle. With a D CAD program, I can rotate the model around and see how much clearance there is around the parts, visualize it from the front as well as the side, etc.

Originally Posted by Joe Perez

I can rotate the model around , visualize it from the front as well as the side, etc.