Imposing price controls impedes on this freedom, thus placing obstacles to mutually beneficial trades and decreasing wealth.
To demonstrate this feature in my class I give students demand and supply curves, allow them to buy and sell a hypothetical good, and assign them grades based on their profits. In two trading sessions I imposed price controls. One time I enacted a price floor and one time I enacted a price ceiling, and in both cases the overall level of wealth statistically and unambiguously declined.