Beer "salts" is, as you may know, a generic term for the various additions (chemicals) you can add to the mash. It is my understanding that many of the "salts" are intended to match the water makeup, or profile, of the region from which the beer style you're brewing originated. These "salts" cause the various enzymes, and other compounds, within the mash to react differently than they would without the particular addition. The result of these reactions are, in part, what delivers the flavors and mouth feel of the particular style of beer you're brewing.
Ever wonder why certain regions in the world are known for producing a specific style of beer? Porters and stouts from Great Britain, Pilsners from Plzen, Czech Republic, etc.? This is largely due to the water makeup of the specific region, according to John Palmer in the book: Water, a Comprehensive Guide for Brewers.