The pitch differential is the difference in elevation between the heel and the forefoot, sometimes referred to as "the drop." Most traditional men's dress shoes sport an offset heel design that raises the heel anywhere from 10mm-20mm above the forefoot. So what's the problem?
An offset heel such as the one you see to the below promotes HEEL STRIKING, a major cause of ankle, knee, hip, and back pain. Making heel-first contact during your stride isn't natural from a biomechanical standpoint and it sends the kinetic energy created at impact up your bone structure. As a result, you can experience serious joint pain. A better alternative is a flat shoe that won't impede your natural stride.