In my part of the world salt in tank = no fungus and no salt in tank = fungus, and that's fairly reliable. It's also good for ich treatment. I haven't had any particular problems arrising from the use of salt, tho obviously difficult to tell , but certainly have had problems with the lack of salt. I had long lived rainbowfish and guppies live full lives and the gudgeon just keep going. Neons die on a regular basis but other tetra don't. That might be just the neons and it is possible it's the harder water we have these days. I haven't had any effects show up to cause me to not use salt, but as I always say, that's just my situation in tropical Australia...
so the pros are have been mentioned - slime layer, nitrites, fungus, ich, etc. The cons I don't know of, but interested to hear. I think irritation was one. Not sure. I haven't observed anything myself, but it's a hard thing to test and judge...