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.