It protects value across time, which gives people a bigger incentive to think of their future, and lowers their time preference (this is what initiates the process of human civilization and allows for humans to cooperate, prosper, and live in peace.)
Sound money allows for trade to be based on a stable unit of measurement, facilitating ever‐larger markets, free from government control and coercion, and with free trade comes peace and prosperity.
A unit of account is essential for all forms of economic calculation and planning, and unsound money makes economic calculation unreliable.