Take a very standard New Keynesian macroeconomic model. The two key ingredients (the only ones that matter for this post) are: monopolistically competitive firms; the Calvo Phillips Curve. In that model, if there are no macroeconomic shocks, the equilibrium level of output and employment is below the efficient level of output and employment. Because it is a model where individual firms have market power and face downward-sloping demand curves. A temporary boom, caused by a positive shock to aggregate demand that causes output and employment to increase, is a good thing. But it's only temporary, and the central bank will need to reduce aggregate demand to bring inflation back to target, to prevent ever-accelerating inflation.
Now ban the Calvo fairy, by imposing price controls on all goods, so firms are not allowed to increase prices. Then have the central bank increase aggregate demand. Provided the central bank does not increase aggregate demand too much, firms will increase output and employment and will not ration customers and create shortages of goods. The result is a permanent increase in output and employment, which the model says is a Good Thing.