It promotes healing and return to as normal function as possible depending on if there was permanent injury involved or not. People who do not comply with their physical therapy require prolonged healing time, and put themselves at risk for permanent disability where none might have been had they followed their therapy and exercises.
With exercise and stretching. Massage and often chiropractic measures are also used. This is usually done after an injury or surgery, kinda like a transition from hospital to home or incident back to 100%.