Here’s the harder question that I haven’t seen satisfactorily answered by alternatives to markets:
How many screws should the screw-maker make?
With markets, the answer is that prices are the signal to make more/less screws. The screw-maker doesn’t need to know anything about the rest of society: when screw prices go up they make more screws. When they go down they make less.
Screws are not made by hand today, of course, they’re made by very large and expensive machines that can produce millions of screws per year. When the screw-maker wants to increase screw output but their machine is already at full capacity, they need to buy another machine (and perhaps even another building to house it). Needless to say, this is a very big decision that can’t be taken lightly, otherwise the screw-maker might go out of business.
In a non-market economy, how do decisions like this get made? The advantage of markets is that the decision-makers only need access to “local” information: that is, information about prices of screws and screw-making machines and other miscellaneous details related to the screw-making business. They don’t need to know how the entire economy works as a whole, something central planners do need to know if they’re going to decide for everyone how many screws need to be made.
This simple difference (information on a need to know basis) lets the screw-makers be experts at screw-making, and optimize their business in ways no central planning committee could ever hope to achieve.