Auto repair, the basic primer
Chains cut back on the amount of time you have to wait for the mechanics to get necessary parts because they an afford to keep a large inventory of parts on hand. Chains also have more employees than all but the very largest independent shops, so they have the staff on hand to a two man car repair easily and to speed up repairs by adding more mechanics if the job can go faster with more hands. An assurance of quality is the second reason. Chains hire only licensed and certified mechanics. On top of that, having more mechanics at the shop means having more experience on hand to puzzle out obscure problems, and means it is more likely that you will get the services of someone who specializes in your car's type of problem.