really its just something to expedite bartering, if i have tables, and want a chicken, but the local chicken farmer doesnt want any more tables, really, the only thing she wants is purple dye, and the only thing the dye merchant is really aching for at the moment is a pickle, i dont have to trade a table, for a pickle, for purple dye, for a chicken. i just sell someone a table, then go use that money to buy a chicken.
at least in theory.
in an ideal society, noone would ever take more than they needed, we would be considerate and kind, everyone would contribute what they could and never make more people than we could sustain, so there would be no competition, and no need for money, and we would all serve the mighty overmind, in all its glory.