IMO/E Aquarium salt should not be used long term, it can cause internal damage in some species, namely kidney damage as well as cause resistant pathogen/parasites from over use and use of wrong dosages, also some species of fish and plants can't tolerate salt.
The salt debate has been going on for years and true many years ago salt was needed in aquariums due to the poor understanding of fish and how it related to health and overall well being as well as the understanding of water quality and the lack of good filtration that we have today.
In neglected tank salt can help short term and you will see the fish perk up...however short lived.....
Now that most fish are captive bred most no longer require natural habitat waters to thrive.
Many hobbyist still use long term salt when it is not needed or required and often they will see symptoms like dropsy in some species for no reason and often it is due to system shut down from long term salt or are no longer able to treat parasites effectively like Ich due to known resistant from long term use and wrong dosages.
Both aquarium salt and Epsom salt when used in correct dosage are great treatments for many problems seen in our fish IMO/E.