To be able to add a voucher/package to the customer's ticket. This could happen if the voucher was registered under services, not products. We have customers who, book for a single service, but at check out want to buy a package and use the first session of the package to pay for the received service. Currently the customer needs to purchase the voucher first, and then I need to go back to the check out box to be able to apply the voucher, but it would be easier if I could just change the single booked service to a package and check out the customer with one step.