It keeps you from getting what you don't want.
There's an aphorism about however many ways there might be to be alive, there are vastly more ways to be dead. (Sometimes expressed as observing that to a first approximation, every species is extinct.)
Systems can handle the small number; the list of things (being subject to violence, privation, ignorance, and want) you wish the system to prevent. Maintaining the core goal of civilisation -- that you die, on the odds, of something that isn't starvation or violence -- is simple enough to build a system to accomplish.
A system that guarantees you get what you want isn't simple enough to build. A system that gets you what you want, or worse, the entirety of what you want, is required to dispose of the constraints that would require you not to oppress everyone else, since it's impossible to constrain it not to oppress them into the violence-privation-ignorance-and-want space and still give you whatever arbitrary thing you desire, too. So you wind up committed to the oppression as soon as you expect direct, positive outcomes from your society.
(There's nothing wrong with wanting things, or trying to get them, but you have to stay in the "no causing violence, privation, or want" constraints of civilization when you do it. Move outside that -- try to make society a guarantee and a surety of your specific desires -- and you're going wrong.)
We're suffering from a long period where policy has been to give the rich what they want. It's distorted everything into increasing general suffering, privation, ignorance, and want in preference to finding a way to tell the rich no, you can't have that.
The simple-enough-to-work fix is "no rich people". We know getting clever with feedback doesn't work; we're living in the failure of the mid-twentieth century attempts to do this with feedback. Time to do it with constraints.