Manual drawing has a tradition so old that it disappears into prehistory, while CAD (computer aided design) drawing was unknown even 50 years ago. Each of these methods of creating visual imagery has its advantages and disadvantages. The discriminating artist understands which technique is more suitable in different creative conditions.
Particularly in the case of architectural drawing, repetition of identical components is sometimes required. The capabilities of CAD technology are designed for this situation and are far more appropriate for it than hand drawing. Using a CAD program, the artist or designer can create a single window or other feature, then replicate it as many times as necessary. This repetitive quality would not necessarily be a strength in some artistic applications but is definitely appropriate for use in mechanical drawing.
The design of buildings, machinery and other technical components requires extreme accuracy, sometimes to the thousandth of an inch. Achieving this level of accuracy while drawing by hand is difficult and exhausting. CAD technology accomplishes it by adjusting the level of accuracy of the grid on which you are working in the program. You can set up CAD programs so that drawn lines are "snapped" to the nearest appropriate grid line, resulting in perfectly accurate measurements. In high-tech applications, the CAD program is fed directly into a manufacturing device such as a computer numeric control router, all but removing the risk of human error in the manufacturing process.
Emotion and Creativity
In the realm of emotion and expression, CAD drawing loses its edge to the touch of the human hand. While not able to replicate elements instantly or draw perfectly to the thousandth of an inch, an artist's hand can still create emotive works that are beyond the capabilities of a machine. Convincing representations of the wavering lines of a growing tree or the smooth curve of a woman's hip are dependent on the artist's eye and hand and the awareness that connects the two. The human complexity and imperfection that reside in the artist, the same qualities that are disadvantages in the realm of technical accuracy, are what create the artistic mystery that is beyond the realm of a computer.
Serendipity vs. Perfection
Beauty and innovation are often the results of events that are originally seen as mistakes. The accidental but fortuitous discovery of something wonderful is known as serendipity. In the perfect and linear interior world of a computer, serendipity is virtually unknown. The binary perfection of which a computer is capable leads to sterility in the absence of creative evolution. Hand drawing, practiced by a sensitive, conscious and talented artist, remains subject to the guiding and unpredictable hand of fate. This hand retains the ability to make mistakes and, consequently, to discover the unknown.