I work for a university, and they're pretty big on paper receipts for expenses, as well as money incoming. It's more about auditability, I think. To be able to say to the IRS, shareholders, the government and even internal management that the money spent in transaction ad9c538e was spent buying servers, and that five years ago those same servers were fully depreciated and sent off for ewaste / recycing, and here's the documentation to prove it.

Otherwise, you're potentially taking too much depreciation, opening the door to employee theft, and making managerial decisions based on poor data. Paper / letterhead is some kind of proof that can be followed up with. Even if an employee fakes a purchase, does Dell have a record of purchase order #2023420? They don't?

An electronic version of this stuff would be fairly useful, but is sort of a collective action problem: if vendors offers API nobody uses, was it worth the effort? How do you handle N vendors offering N different APIs? And how do they upgrade when they interact with hundreds of clients?

Collect early, pay late.