And the way the salt "tastes" is different because the powder dissolves on your tongue differently/quicker.
Salt "dust" is a really interesting way of adding salt to food -- and you actually end up adding less than larger grains
I've never seen on-the-spot ground salt smaller than the stuff you can buy already grounded. Except if you buy flakes, but then why do so if you want finer salt?
Therefore, grinding things at the last minute makes them taste better, goes the simplification.
Therefore, grinding salt must make it taste better.
But salt is not like the aromatic flavors in a peppercorn. Salt is geologically stable. NaCl itself does not need a last minute grind to retain its salty flavors. NaCl is not a chemically complex flavor.
I qualified that as NaCl specifically because it is faintly possible some of the fancy salts could have their fancy flavors come out better if they are ground, but I'm yet to even notice a difference when any of these are used in food in any manner so I can't judge. Those flavors must be awfully darned stable as it is if they're still hanging around in a 99+% NaCl environment. I'd want to see a specific chemical that can survive that but will suddenly wilt if exposed to oxygen. (We're sure not talking about traditional benzene-ring aromatics at that point!) If there is a difference it is hovering at the very bottom of human detectability.
Salt grinders are annoying. They're hard to use because you're trying to grind a rock, a soft rock sure but still a rock. It's wasted effort, and it occurs to me to wonder if they even do anything to speak of; now I want to find one and compare the before and after of the chunk size; I find myself suspicious that many of them are just theatrics and the salt basically passes through unscathed because "cheap plastic" and "grinding a rock" are not compatible with each other. Even if it does do some real grinding it's still a waste though because it was never necessary, you could just have bought it at the right grain size.
Usually you'd just use two sizes of salt. I don't own a salt grinder, can't remember ever seeing one in a professional kitchen, don't recommend people buy them. But it does produce a particular effect that you could prefer for some applications.
And in fact I suspect popcorn might be one of the places where it would shine. An even background of salt dust with bursts of intense saltiness from larger grains sounds good here. I'm not going to buy a salt grinder to test it but it's not an absurd idea.
I think you’re misunderstanding the use. It’s a different goal from grinding spices. It’s functional. And I’ve never seen powdered salt selling anywhere in Canada. (Except for expensive artisan stuff). So, the best way to achieve it is with a grinder+rock salt. I’ve been using a simple Amazon grinder and it’s easy to use.
Powdered salt tastes different not because of a differing chemical composition, but because of its different physical nature + your tongue.
Or... it's an after the fact rationalization for the cargo cult!
At best this might be your goal, for whatever reason. 99% of the people who cargo cult a salt grinder don't have that reason - and regular sold salt would be 100% OK for their purposes.
Right off the bat any real consideration will make you aware that large particles will distribute very differently from small particles of the same volume.
Additionally that large particles will be substantively different from small particles in how they interact with the toungue. Eg large particles will "burn" more due to their extreme concentration and will be effectively "hot spots" of seasoning.
From just that it would be apparent that there would be truth to the claim of substantial difference in experience when using the two forms.
Right?