Physical therapy may be one resource that enables a child with issues of proprioception (the sensation of feeling disconnected from one's limbs and trunk in space) to feel better connected and at peace in his body. Challenges with fine- and gross-motor skills and repetitive actions, activities or vocalizations are hallmarks of autism.
Remember that the true purpose of any therapy is for the therapist to impart his or her skills and expertise to you in a way that is easily replicated into the flow of your family's natural, daily routines. Physical therapy applied only by a therapist for a limited timeframe once or twice a week will accomplish very little as opposed to embedding physical therapy techniques in your child's typical routines every day.
Are there therapeutic activities that can involve siblings or neighborhood peers through swimming, or games that involve climbing, pushing or pulling, or mimicking animal postures and movements? In this manner, physical therapy becomes invisible---and fun!