I don't know that it is a recommendation, so much as it is what was/is in particular brewing water associated with IPA's.
As for what it does..... I can't say that I have compared blind using and not using salt in beer in the range of 0-50ppm. However, it is said that it can "round out" a beer. I have been brewing a lot of IPA's recently with higher CaCl, NaCl in the 30 range, and lower sulfate. Those beers definitely have a rounder hop perception. Now..... is that just the 30ppm of salt.... probably not. It is also the higher CaCl, the lower sulfate, the higher pH (5.4ish) etc.
But, at least in conjunction with those things, that is what I observe in my beer compared to the traditional high sulfate IPA profile.