Salary negotiations are a very simple example, you can easily compare your salary to that of your peers and to similar positions in other companies. If your boss tells you they pay you the industry average or company average or whatnot, you wouldn't be able to check whether that's actually true otherwise. You can also have a rough ballpark of what a company pays before you apply for a job there. In general, information like this being public empowers people, whereas in most countries companies hold all the cards and use this information asymmetry to their advantage.

OK, you see that your peer earns 2x more than you, then what? You automatically assume that you need to be paid the same?