LABELING DIAGRAMS HELPS YOU VISUALIZE SOLUTIONS. Physically diagramming information is an effective way to move through it mentally because it forces you to interact with the diagram. Once you've moved through information, you can visualize it from different angles, make the right assumptions, and know instinctively where to approach it.
Obviously, trying to diagram or rewrite every problem on the test is not an effective use of time. Such a heavy-handed, dogmatic approach restricts your movement. Your movement is only free when you allow the characteristics of the problem to determine your approach. For example, labeling a geometry diagram may help you discover a radii or a bisecting angle that you can use in another part of the diagram. But rewriting an algebra problem could be less effective than simply plugging the possible answers into the equation. As you study for the test, observe the different situations in which these tools are most effective.