Will medical charting wonders never cease. This kind of diagramming makes perfect sense in a medical setting. When a patient comes in complaining of a particular symptom, sometimes it's like taking a car to a mechanic -- the symptom doesn't show up, or doesn't seem to mean anything by itself.
However, using a Wigger's diagram helps a doctor understand when the patient is experiencing this kind of symptom, something else may be happening at the same time, which the puts the symptom in context and enables the doctor to diagnose the patient more accurately. And of course, an accurate diagnosis means better treatment.