Simple concept with big implications: In small groups, money corrupts.
In environments that are built on personal interaction and trust among intimates, transactions based on money don't increase efficacy, they degrade it.
At the other end of the scale, in transactions between strangers, cash scales. Cash enables us to interact with people we don't know and probably won't see again.
But if you want to build the intimate circle that lives on favors and gift exchange, don't bring cash. Bring generosity and vulnerability.