Some freshwater fish may have a low amount of salt content in their natural habitat, but unless you know what it is and you have a hydrometer to keep it that low, its best to go saltless unless the fish are ill in which case salt is your friend. Using salt with ill fish is proven to help, but using salt with freshwater fish who are not ill does nothing. It just sells more salt.
You may see a container of salt in the tanks at your lfs. This is because their tanks are disgustingly overstocked and very likely that several fish are infected at any one time even though the illness is not yet visible.