If a therapist has regular scheduling, when someone can't/doesn't come there's a blank in his schedule and an independent therapist might only want 3 clients on Monday, 8 on Tuesday, etc. The way the HMO (which is both the insurance company AND the therapist, the therapist is assigned to the company and works for the company) the therapists get a regular schedule (9-5 Monday through Friday, say :-) but, there aren't any blanks because each space is filled week-by-week and any would-be blanks are taken up by first-time/new clients.

The HMO tells the therapist how often they will work (and/or can hire more therapists and pay one who works less, less money) and gets optimal scheduling, like how stores schedule their employees (when I went to Sears Roebuck manager training that was the part I loved; you had to do word problems, "The store is open these hours, you have 5 employees, these 3 are full time/work 40 hours and the other two are part-time, PT-1 is a student with these X hours free and PT-2 is a housewife with kids that can only work 10-2 every day").

My T use to charge for cancelled appointments (less than 24 hours) but if I went on vacation, it's not like she could put someone else in my slot because it was "mine" so she lost income when I was away. Too, it was hard to adjust her individual schedule, she had to plan years ahead she said for people to terminate, or to change workplaces, locations, etc. With the HMO, the therapists can adjust their hours, it's just harder to get an appointment with them (because that person might have fewer hours than people who want to see him).