The course is the unit. How many sessions were bought, how many remain and when the package expires has to be visible at the desk, because a client who has lost track is a client who feels cheated.
Intervals matter clinically. Sessions too close together achieve nothing and sessions too far apart lose the benefit, so the booking system has to know the right gap rather than offering the next free slot.
Consent and patch test records are not optional. What was assessed, which settings were used and how the skin responded is the file that protects the clinic if anything goes wrong.
Unused sessions are money already taken and work still owed. Knowing how many are outstanding across all clients is both a financial fact and a marketing opportunity that most clinics never look at.