The Medical Director can edit all aspects of a patient's record, and importantly manage the vaccine, disease and country information contained in Inca. See Inca Clinic - Medical Configuration for more information on how to do this.
The Medical Director Profile is useful when the roles of System Administrator1) and the management of medical information are performed by different people. In small to medium sized clinics, the Medical Director and System Administrator are often one and the same.
The Medical Director has many but not all the abilities of a System Administrator. For example, the Medical Director Profile cannot add new users, or manage Inca Clinic licensing, etc.