A brake cable blunder made me start drawing repair diagrams
I figured sketches were a waste of time. Then a guy at the shop installed his front brake on the rear, and my simple picture cleared up his confusion. Now I sketch out repairs for all my clients.
Last year my buddy got hit and his insurance claim got messy because he had no proof of the original repair work. A clear diagram from the mechanic showing exactly what was done would have saved him thousands. That mechanic isn't just fixing your car for now, he's creating a record for any future problems or accidents. If the work ever gets questioned, those notes protect both of you. So yeah, he needs a good diagram to cover his own work, and that ends up covering you too down the road. It's less about who needs it more and more about it being a necessary part of the job.