Getting your money later means that your you are effectively giving out a free loan to whoever is holding your money. For you that's an opportunity cost because you can't reinvest the money for some period of time.

If your expenses have to be paid before you get your money this can also be a cash flow issue (or make a cash flow issue worse), when a peak in demand leaves you very profitable but unable to pay your bills because you're waiting for your money to arrive.

Yes.

In credit card world it goes auth, capture, settlement. Auth happens within those few seconds when you slide your card. Capture tends to happen at the end of the business day when the "final" total is known and charged against your card. Settlement is when everything has cleared and merchants get their money.