Availability belongs to a person. A room is useless without a qualified therapist, and treatments requiring specific training narrow that further, so the diary has to be built around who is working rather than how many rooms exist.
Turnaround is unpaid time that must be scheduled. Stripping a couch, airing a room and preparing oils takes minutes that disappear from the day if bookings are placed back to back.
A course paid up front is a liability. Six sessions bought in January and used across a year is money received and work still owed, and a spa that treats it as income has spent something it has not yet delivered.
Retail matters more than it looks. Products recommended after a treatment carry margin the treatment itself cannot, and recording what each therapist sells shows where a conversation is happening and where it is not.