1. Unlike belts they can transmits large amounts of torque
2. Unlike meshing gears they don't need to be constantly lubricated
3. Unlike belts and mesh-gears the spacing between centers can be easily adjusted by shortening/lengthening the chain
Despite these advantages, few people know how to draw sprocket gears, which are designed based on pitch rather than mesh.
Step 1: Get DraftSight or other 2D CAD
For those who learned how to use, and are hopelessly addicted to AutoCAD's GUI, I might note that DraftSight has the look and feel of classic AutoCAD without the $4000+ price tag.
Step 2: Determine your Key Dimensions
I will be demoing 40 tooth #40 chain, which has a Pitch of .5in and a roller diameter of .313in.