I've yet to see anything proven that it helps at all unless treating ich, heavy nitrite poisoning, etc. It's not something, in my opinion, that NEEDS to be added. Might as well save the time and money...
It can be used for quarantine procedures to destroy a wide range of parasites such as flukes and ich aside from combining it with praziquantel. I would not however advise using it on a permanent basis. It's practically a waste of time and money.
Few plants do well in salt. Java Moss and Java Fern tollerate it amazingly well, for me.
In the last 3 to 5 years, I have never seen salt work for ICK. Long ago it did. I can only imagine that ICK was able to become salt tolerant, or else somewhere along the line we got a brackish form/sub-species imported which can.
Unless I had brackish water fish, my use for salt has pretty much disappeared.
However, that said, I have had some luck in removing Utricularia from my Java Moss with salt; and, of course, it will still kill snails.
Not sure what you mean by silver tipped sharks but none of the others need salt. Your "shark" could be a Jordan's Catfish, Arius jordani which would most definitely benefit from salt. I'll track down a pic and post it in a minute so you can see.