Or Beer or Wine Currency.
That is, you ask someone to do something for a coffee. And of course they say yes.
However if you asked them to do the same for the equivalent monetary value, would they do it? Probably not.
It swaps the value proposition, oh I can get a bottle of wine for this? Awesome that’s not too hard. Whereas if you said I’ll give you $20 to do this, the internal memo is different “I’m worth more than that”, “that’s not that much” or maybe it is worth that much.
MySpace have a great example with some of their competitions, whereby you can win three prizes (don’t hammer me on exact details if I’ve made a mistake), a pinball machine, a holiday, a quad bike or $5000 cash. Apparently the Pinball Machine gets disproportionality picked, even though if you took the $5000 cash you could buy 2 or even 3 of the other prizes!
The point is once someone receives money they need to do something with it, a Pinball Machine is much more fun than paying off some bills (which many would be compelled to do).
People interpret currency differently and you can (should) use this to your advantage where possible. My Dad famously (at least in Queenstown, New Zealand) is always owed a coffee by someone, which he then trades up to something even more valuable…