Back in my aquarium shop days I was under the impression that salt was a matter of total dissolved solids and the slime thing. I do have to say that I felt salt has it's place. I typically didn't add salt but for a few problem fish. I went to a tablespoon or two or rock salt per 10 gallons, along with a half dose of tetrid (I think that's what it was, it was back in the 80s) whenever I got a batch of new neons, worked very well. I also used to salt the heck out of my feeder goldfish. We had a supplier that sent feeder goldfish to all the shops in town, I had a different guy I got feeders from part of the time that said they really do well with salt, I went to doing a 80% WC on my 40 gallon feeder tank with cold water and adding a bit over a 1/4 to 1/3 cup of salt right before adding the feeders, went from heavy losses to virtually none. There was a significant amount of time I was the only store in town with healthy feeders, even though we all usually got them from the same supplier. I typically brought in 2000-3000 feeders at a time. It was a bare 40 breeder tank with the biggest marineland bio-wheel HOB available at the time.
I have zero problems with a bit of salt in most tanks, with allowances for certain fish or plants. Guess I'm old school. Don't know if I'd bother adding salt on a regular basis if I was having no problems with my fish.
I'll mention, I haven't had an aquarium in years, just getting back into it (hopefully, long story, too busy scuba diving to bother with an aquarium these days, hope to change that) so a lot of my training/upbringing is based on 60s/70s/80s/90s info, thought have changed the last 15 years or so on some things.