A course of ten sessions sold is not revenue until it is used. Showing the sessions left, to both sides, brings the client back instead of letting the package expire quietly.
Product used in the room — colour, gel, disposables — never appears on the price list. Logged at the appointment itself, what a treatment really earns stops being a guess and becomes a figure you can price against.
Rooms and staff are two resources on one calendar. Booked together, the double booking that shows up at reception disappears before the client does.