The other booking platform I used had this feature and it was helpful to be able to ensure the funds were there in order to avoid a Declined Card error after a cleaning is done. In my business, we only accept credit cards, so I don't send invoices. It is especially helpful to know that the funds are good on that card. If the funds are not available, I can contact the customer and get updated card information or cancel the cleaning if they can't pay for the cleaning.