It’s entirely different, because you are transacting in the same currency without an exchange mechanism required. This is important in days like today, where

It’s entirely different, because you are transacting in the same currency without an exchange mechanism required. This is important in days like today, where a coffee would cost more in BTC this evening than it would have this morning - how do I know how many BTC I have spent without referring to the current market price in USD and calculating it?