Infinitely divisible money is an unit with unlimited ability to scale to the circumstances - if more is needed, simply add another zero. You err in comparing this to roads, which are necessarily in proportion to the amount of traffic over them. Money needs only to be able to represent value, and the relative value of different things.

Good monetary policy may be practicable by angels or saints, but not by men, who stand at the gates of unimaginable wealth that emanates from the printing press. Literal trillions of dollars - who can even conceive of that value, let alone decline the exercise thereof? Better to take it out of our hands.