Previous clients come back
Income vs profit (how much you need coming in before you make the amount of profit you need, to give an indication of how much you need to sell)
Find out where people found you so you can see if your marketing works (eg found through advert on instagram, that would mean you would know the exact cost to get a new client from there).
Individual treatment % to find what is popular
Upsells, cross sells, retail, rebooking. Eg each member of staff say they had a facial booked, and how often did each one upgrade to include eg a lip wax and brow tidy and sell a facial kit then get client to book next appt
How much money each group of treatments makes (men’s/women’s/waxing/skincare).