Follow one invoice through a manual AP process and count the touches. Someone opens the email and downloads the PDF. Keys the vendor, invoice number, date, and amount into the accounting system. Looks up the PO, if there is one. Decides which GL account each line belongs to, or guesses, or pings someone who might know. Forwards it to an approver and waits. Follows up. Waits again.
One invoice looks harmless. Multiply it. If a touch-heavy invoice takes your bookkeeper ten minutes and a few hundred land every month, put that against their loaded hourly cost and the number stops being cute. Then add the part that actually stings: the duplicate that got paid because two people keyed the same PDF a week apart, the early-payment discount that quietly expired in an approval inbox, the close that slipped because nobody cleared the pile in time.
None of this is accounting. It's typing, looking things up, and nagging people, and every piece of it can be read, decided, or escalated by software instead of by the person you hired to close the books.