When a coupon is made with maximum uses per customers. Then one would expect it to check the database for an order from that customer (and we have the email). Or at least an option: if not logged in, check email too.
So the option use coupon once only counts logged in customers
When there should also be a check for (unique) email counts per order for guest checkouts
This would be great to add. We have a customer who has ordered every month the last year with a coupon code that can only be used once per customer. It is not closed loop solution: but checking for an already existing order from the email you would solve 99%