Q1- The concept of proportion is drawing something to size. It is used in sketches to give that 3 dimensional style, a whole new look. It makes the object being sketched, look 2x as realistic, compared to an out of proportion sketch. Q2- Creating realistic sketches can make a person a more competent designer by providing them with a clearer perception of what they're designing. A consumer would be more likely to buy a clear depiction, over a sloppy doodle. Q3- If someone were to design a complicated mechanism, there may be tricky parts to explain with words; therefore, a blueprint, or other drawing, could be used to clarify what is trying to be explained. Q4- I believe that shading is the most important part for creating a realistic sketch. If you have the basic shapes, you can shade them in to create a more life-like object.