the main difference is $$ and quality. if you were rear ended by someone else and if they are going to pay for the cost of your repair, then why not go to those dealer approved body shops to get your car fixed? if you're thinking of cash settlement but still taking your car in for repair out of the money you made from insurance claims, then you can consider going to those mama papa auto body shops. they will most likely still do a good job at a lower price, but may either take longer time or with somewhat of lesser quality.