Non-EDI doesn’t mean small. Some non-EDI trading partners are small businesses, but many are large companies that never set up EDI for your relationship, use it only for some documents, or rely on email and spreadsheets for complex steps such as order changes, claims or detailed shipment notices.
Non-EDI suppliers and customers create manual work on your side. Someone keys their orders, confirmations and invoices into the ERP, chases missing documents and corrects errors after the fact. Their transactions also tend to sit outside your reporting, so a late confirmation or a mismatched invoice is found later than it would be for an EDI trading partner.
Requiring every trading partner to adopt EDI is rarely practical. The more common approach is supplier enablement that gives each non-EDI trading partner a channel it can use, such as a guided web workspace, spreadsheet upload or document digitization, while applying the same rules you apply to EDI.