Timing belt replacement and much more
The first reason is speed. 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 larger staffs, so if a repair is a two man job or it's possible to speed up the car repair by adding extra mechanics to the job, the repair shop has the people to do the job. An assurance of quality is the second reason. Chains hire only licensed and certified mechanics.