Medical science depends critically on knowledge of human anatomy. Application of this knowledge allows health professionals to perform important skills necessary for preventing, diagnosing, and treating disease.
As an example, one of the cornerstones of preventive medicine is the annual physical exam. A proper head-to-toe exam requires that the examiner be aware of anatomical landmarks that can be inspected, palpated, and otherwise investigated to rule in or out a particular condition.
If palpation of a particular region elicits pain, discomfort, or reveals a mass or other abnormality, anatomy can clue the examiner in to what may be going on beneath the surface. For example, pain in the lower right quadrant might suggest appendicitis given an appropriate clinical history. A nodular mass felt above the left clavicle might add gastrointestinal cancer to the differential diagnosis.
There are countless examples, but you get the idea.