They use this system at the National Festival in Canberra, Dazbo, and (because the staff didn't have to find change) it really did cut down on what would otherwise have been huge waiting times with so many people trying to get served at one time.

The drinks weren't all the same price, but the pricing was certainly simplified. You bought a string of tokens (I think they were $2 and $3) and that enabled you to produce the correct amount for whichever drink you wanted. I don't remember left-over tokens being a problem!