The primary aim of the test is to measure aerobic capacity or cardio-respiratory fitness. Many studies have been done showing that the beep test is a good predictor for the maximum amount of oxygen a person can use (also called VO2max).
It is therefore used by many organsiations and individuals as a way of measuring aerobic fitness - for example to provide recommendations for healthly living or minimum fitness levels needed for entry into certain professions (such as militatry forces, the police, sports etc).