Though I am capable of producing intricately detailed plans on either CAD or by hand, I have never found them necessary. Fifteen years ago, when I began making custom furniture, I would put in quite a bit more detail than now. For me, the precision measurements do not have to be written on the plans in order to create a wooden joint that matches seamlessly, even to the touch. In fact, often, I will find a particularly stunning piece of wood grain and alter my plans slightly to include this figure in a piece. See also, How was this made? and Cherry "Star" table detail and construction to see what can be made and how it is made.
This is not to say that standard measurements and conventions such as dining room tables being between 29" and 30" high should not be adhered to. A good furniture designer must know the height and depth parameters of a comfortable seat, or the amount of elbow room required at a table, etcetera. Yet there is often a compromise to be reached between the clients needs and desires and conventional design parameters. All of these factors are important to discuss prior to finalizing and ordering custom furniture.
Below are various drawings I have done in preparation for a piece. If you are able to draw or sketch, don't hesitate to write down your ideas! People are often delightfully surprised to see a fine piece of furniture and then see the yellowed and slightly smudged sketch from long ago that aided the development of the piece. That's part of the fun!
