Wasn't there another rules like this, disclosure of C-level compensation, that had the opposite intended effect. That is, once everyone's compensation was made public, it just turned into a top level dick measuring contest which, in turn, resulted in a compensation arms race in which everyone was trying to be the new top dog? It's good information for the employees to see how far beyond them the CEO is, but without some way to improve employee mobility, it seems like it'll be more of a slap in the face than anything.
Yes, I have my doubts that it will be effective. It's not as if similar information is difficult to find. In a worse case scenario, it might normalize the disparity. But, as an investor, this can give you some clues to the company's strategy, especially when compared to others in the sector.
This is true, but there is a little more to it. While this is for public companies, I imagine that there is hope that it will foster social pressure on private companies to be a little more open, much in the same way supply chain transparency and carbon footprint data does.