Some products do not suit paying in full at checkout. Made to order furniture, a pre-order six weeks out, a high value item a customer wants to reserve. Standard checkout forces the whole payment now, and you lose the orders that were not ready for that.
Downpay handles deposits, partial payments and pre-orders inside Shopify's own checkout, which matters because a separate payment flow costs conversions. We set up the terms per product, connect the balance collection to your fulfilment timing, and make sure the customer knows exactly what they have paid and what is still owed. Getting that communication right is most of the work.