Face transplants are a new concept in plastic surgery. They are viewed similarly (from a medical standpoint) to a kidney transplant or heart transplant. Patients are on immune suppression for their whole life!
Face transplants are reserved for patients with disfigurements SO severe, that all of our efforts, techniques, and tricks for reconstruction (like skin grafts or flaps from other parts of the body) would not restore a normal or even recognizable appearance to the face. Some people look so disfigured (SAD!) from severe injuries like animal attacks (the first face transplant in the U.S. was from a chimpanzee attack) and electrocution, that they are viewed as monsters (SAD!) by society.
A face transplant is a microsurgical procedure. That means that small blood vessels are sewn together to bring blood flow into the transplant. Also, the face comes from a patient who has recently been deceased (or in whom brain death has been established). Very complex stuff!