I switched to cutting my own hair (and modifying my hairstyle slightly to make that easier) exactly because of the time wasted sitting in the lobby. I don't mind the value-added time (when the hair is actually being cut/styled), but the non-value-added time was too high for me.

I switched dentists for a similar reason; prior dentist kept a buffer of patients waiting to optimize their throughput. I had a dental appointment yesterday [at the newer place] and I was annoyed that I arrived 15 minutes early, because I know they make it a point to bring patients in exactly on time. Sure enough, 2:00 hits and I get called back.