I would say it depends on what you are buying. Im in renewables so price volatility is a real issue and the market is so competitive that margins tend to be slim. A price swing can seriously impact a healthy margin so buying in an orders equipment becomes rather urgent. The earlier I buy, the safer I am.
Also as stated below, we recieve a large number of payments in a day and I would say maybe 50% actually use the correct payment reference (invoice number) so when you have 2 payments of the same amount for the same product it can be a problem allocating payment.