The series is the business model. When the next appointment is booked before the patient leaves the room and a reminder goes out a few days beforehand, the rhythm stops depending on anyone's memory.
Treatment plans need tracking. Date, sessions planned, sessions remaining: held in the system, nobody discovers at the last appointment that the plan needed reviewing three visits ago.
Appointment lengths are not equal. A routine check, a nail brace and an orthotics assessment take very different amounts of time; set in the diary, the afternoon stops backing up.