ummmm...
well, its the same as drawing except its rougher
people abstract ideas landscapes cartoons scenery So really you can sketch anything u like....its all up to you.
CAD sketches are more accurate and precise and they can be communicated faster and easier
CAD is a software which can lose information and must be learned to be properly used. Also, freehand sketches can easily have information be added.
They are wayy better
It is not that very detailed.