Why is having a black market good? Is it that there's inherent value in making a market for something people find valuable (even if the seller is some tech pers

Why is having a black market good? Is it that there's inherent value in making a market for something people find valuable (even if the seller is some tech person and the buyer is a dissident in a country that probably can't legally send money to San Francisco in the first place), or is it something else?