I would dare say that this is when you have too much of salt in the system, or for too long. Because salt has always been a good treatment for parasites, bacterial infections and so forth. And in one of my books, in the sickness section (which a veterinarian wrote) salt is recommended almost always when you can't find a reason for the fish to be sick!
It relieves the pressure on the gills, for example, in case of treatment of wounds or water quality problems with nitrite, although it slows down the filter bacteria.
But yes, it makes the fish stressed when you add it and they're not used to it, but at the same time, it will take care of parasites or bacteria. It works much as when a person uses salt dissolved in water for desinfecting various wounds (like a piercing).
Overuse of salt has also created a few strains of more resistant parasites (Sorry, I can't remember their names) but in Japan, they use no other medication than salt, and let nature do the rest.

So I think this is not about salt as a treatment method, but more as in the use of marine salt. So YES, it shouldn't be used unless you're treating for parasites or disease. Keeping a constant amount of salt in the tank isn't very advisable.

Yey, you make many interesting threads!

Like I said in a previous thread, you don't have to feed the goldfish in 14 days and they'll be fine (:

I would REALLY not recommend any feeder block for being away for less than two days, really d: They would most certainly rather pollute the water and probably make your fish sick... so rather leave them completely without food during the time you're gone!

Feeding blocks are designed to dissolve and let out food for the fish, right? And having a big piece of food gradually dissolving in a tank (especially such a small one with only two fish) is really not to recommend

But yes, I recently added a bit of salt to my tanks too, and for a moment when I added the salt there the fish reacted really quickly and started swimming fast. After a few minutes they calmed down, though. But they ARE freshwater fish after all

On a nice side note: I'll be saving up a bit of money for the 317 liter tank now! (: I got a great deal with free gravel, filter and lighting! And also 20% discount on EVERYTHING I need for the tank the first month! (Water conditioners, medications, foods, filters, plants...) I wonder when I'll be able to get it!
And I went to the other pet shop and got myself the orandas, but I asked them to keep them there for 2-3 more weeks, so I hope I'll have the big tank by then, set up and with my first 4 fish in it so I can quarantine the orandas! (:
It's a chocolate-blue oranda of sorts, and a white one with red back and partially red headgrowth! They're so sweet <3 I decided to name them Choco and Raspberry! (Might add "Sargeant" or "Captain" before their names at some point for the lulz.)