Freshly ground salt is better for the people who sell those fancy salt mills and combination salt-and-pepper grinders in so-called gourmet shops.
The idea seems to be that if freshly ground pepper is so much better than the powdered stuff in cans, then why not use freshly ground salt as well?
That’s a delusion. Unlike pepper, salt contains no volatile, aromatic oils to be released by grinding. Salt is solid sodium chloride through and through, so a small chunk will be absolutely identical to a large chunk in everything but size and shape.
The fun of a salt grinder is that it deposits coarse little chunks, instead of tiny grains, on your food, and therefore delivers a burst of saltiness when you bite them.
But it doesn’t matter how “freshly” they were ground.