Have you ever submitted a payment or received a payment and seen it marked as "pending". That's likely the result of a delay due to interbank transfers. Real time settlement is something theoretically possible with central banking using something like Fedwire, but in practice most banks use a third party clearinghouse like CHIPS. Additionally, if you have funds in USD and you need to make a payment in EUR, you'll probably need to work through a third party bank that deals with forex settlement. This all adds delays and costs.

With Ripple, realtime clearing and settlement happens automatically even between currencies. If my bank and the vendors bank both use ripple, I can use USD to pay the vendor EUR in real time, and the transaction completes in seconds.