You may have already figured out why CAD has many advantages over manual drafting. One big advantage is that once you've drawn something, you shouldn't have to draw it again. If you manually drew a house plan, you would have to draw a front elevation, side elevations, and possibly a perspective view. With one 3-D CAD model, you can generate views from any angle either inside or outside the house and animations. Afterwards, if your client needs something changed, you can then make the changes once. If you're drawing mechanical parts, you can generate virtual prototypes or even create rapid prototypes. In this manner Boeing was able to design and prototype the 777 jetliner. This level of engineering would be impossible without CAD.
If there is interest on how to convert an old, hand-drawn paper drawing: i.e. architectural floor plan, mechanical, electrical schematic etc.into an accurate CAD file without scanning but using a tablet