1. Diagrams can group all information that is used together thus avoiding large amounts of search for needed elements. Text only indexes to the next element in the sentence list (the adjacent piece of information) while diagrams have many adjacent elements. 2. Diagrams explicitly preserve information about geometry and topology, whereas text is only serial in nature. This feature of diagrams allows for easy indexing of information to support computation processes. However, text preserves the temporal or logical sequence of information. This is lost in diagrams. 3. Diagrams use location to group information about a single element, avoiding the need to match symbolic labels. Diagrams automatically support a large number of perceptual inferences; the information can be indexed in a variety of manners. It seems reasonable that these conclusions, made about diagrammatic representations, can be extended to all graphical representations. Based on Larkin and Simon's conclusions it is easy to see why, in the complexity of mechanical design, drawings are preferred over text.
Later in this paper we will analyze all the marks-on-paper made by a small group of engineering designers. Their drawing marks will be classified as either free hand (sketching) or drafting marks. The hypothesis above states that the sketches have a role that more formal drafting cannot fill. Dan Herbert in Study Drawings in Architectural Design: Applications for CAD Systems [7] considers the use of sketches (study drawings) in the solution of architectural design problems. He defines "study drawings" as "informal, private drawings that architectural designers use as a medium for graphic thinking in the exploratory stages of their work." Architects often make these study drawings in the borders of or adjacent to their formal drawings. In his paper Herbert conjectures about the properties of sketches that affect the design process. These properties form the basis for his theory of the use of sketches in design.
you could just use the 1st 2nd and 3rd reason stated in the beginning. :D
