I'm sure no one is still reading at this point (5 pages into the debate

), but:
I salt my 10g, because it is mostly a gupp nursery with dropping moms and growing fry and from time to time is overcrowded. Salt aids in slime production and that boosts their immune defense.
This tank also doubles as the quarantine tank when needed (rarely), so the salt helps out with that as well.
I don't salt my 29g or my 55g because I am too scatterbrained to keep track of such a large quantity of water and how much water I've taken out/added and how much salt needs to be added. My water changes are kind of random in these two, and I just am too much of a space cadet sometimes to remember whether I've taken out 2.5 buckets or 3 buckets, etc.

I use non-iodized table salt from the grocery store.
In response to the analogy of the plastic bubble, that comparison is a bit flawed. People living in a plastic bubble without any pathogens is the same thing as fish living in a tank with no pathogens; it's NOT the same thing as providing sodium chloride in the tank to aid in osmoregulation. Humans engage in osmoregulation as well, and we likewise require salt in our environment (we consume it as food, rather than swimming around in it, though) to do so. Our first immune defense is also based on the use of salt (in mucous form), which we derive from the food we eat. It's an interesting analogy to say that providing dissolved salt in the water is the same as removing all pathogens in a plastic bubble, but it's kind of comparing apples to oranges.