Brewing salts generally do three things, Ph/RA, add appropriate minerals for yeast health, and the SO4/Cl ratio enhances hoppiness/maltiness depending on what end of the spectrum you're at. I will start by adding appropriate amounts of gypsum, epsom salt, and CaCl to get the right SO4/Cl ratio and the minimum amount of Ca and Mg. If that addition is going to lower Ph too much for the mash, I'll scale it back and add the remainder to the kettle. It's pretty rare for me though. I'm at less is more as far as water chemistry goes, so I don't add salts just for the sake of getting to some city's profile, but I imagine the folks that do that likely have to add to the kettle.