Ordering by WhatsApp works right up until there is a disagreement. Without a written order there is no way to show that you asked for fifteen boxes and were billed for eighteen, or that the agreed price was lower last month.
The real value shows at receiving. Checking the delivery against the order turns a stack of boxes into a verification step, and the differences you find are usually small, repeated, and worth more over a year than most cost-cutting exercises.
Over time POs also build supplier history — total spend, order frequency, and who quietly became more expensive. That is the data you need before renegotiating.
Outale supports POs with vendor selection, line items, internal notes and estimated spend; receiving updates stock through an inflow manifest, and each supplier has a profile showing total spend and full purchase history.