Unless you are keeping coastal species that naturally live with a certain level of salinity in their water or are fighting certain parasites, I wouldn't add salt to freshwater tanks. Few plants appreciate it, and most fish commonly seen in the hobby do best in pure fresh. In cases of certain puffers, gobies, scats, monos; these are true brackish fish and require a certain salinity level to do best. Many of these can live in pure strength seawater (1.026) or water that is barely saline at all, others have more specific requirements. But without a good reason to, it's probably not a great idea for your average freshwater tank.
Nothing good happens fast in an ecosystem.