I had similar lessons in an intro Accounting class I think, they compared the common "2/10 Net 30" payment terms, where you could take a 2% discount if you paid the invoice within 10 days. Annualized, that's a ridiculous rate of return and you'd be foolish not to do it if you have the cash on hand.

If the terms are simply "net 30" with no early payment discount and no late payment penalty, there is no incentive for the customer to pay on time.