Was at a restaurant for lunch today. There were two small grinders on the table. One contained peppercorn, and other contained salt.
I think I understand why freshly ground pepper would be better than pre-ground pepper - am guessing it has to do with surface area and going stale. But freshly-ground salt? Why would that be better than pre-ground salt?
Just a wag: ground salt tends to bake together and clog in shakers because of moisture, so it might be convenient for restaurants to serve it in a grinder. I also see no culinary reason, but I’m open to be educated.
I find it easier to dole out in a grinder. Shakers are unpredictable, and I don’t want to pour it in my hand at a restaurant.
Aren’t they (salt grinders) intended for fancy coarse sea salt with large grains ?
A benefit of (most) salt grinders is that you can adjust the grind size to your desire.
Thats generally where I see them used. Who wants large grains of salt on their eggs?
I heard a chef on NPR a few years ago who said pretty much what you’re thinking. In his opinion salt grinders are just a gimmick. Grinding doesn’t affect the flavor of the salt in any way. All it does is make the grains smaller.
Which affects the texture of your food.
But why not just buy salt pre-ground to your desired grain size? Unlike pepper, there’s no advantage to grinding salt right when you use it.
Peppercorns have oils in them. Grinding them releases the tasty oils. Which is why fresh ground pepper tastes better.
Salt doesn’t have those oils.
I don’t use a lot of salt at home, so it tends to sit for a long time and can get clumped up or the holes clogged. Grinding prevents that.
That’s why I put a desiccant pack in my salt shaker.
I’ve often seen rice grains added to salt shakers to bind the moisture.
Neither of which I want in my salt.
I’m guessing it’s primarily a gimmick intended for the restaurant to have symmetry between the posh looking salt grinder next the posh looking pepper grinder, otherwise providing typical table grain-size salt dispensers would suffice.
The grains of rice are larger than the holes in the shaker so they don’t slide out into your food - my parents salt shakers all had salt in them to prevent clumping.
Clearly you’re not eating correctly. 
It’s true that freshly ground salt probably tastes no different than pre-ground in a blind taste test. But eating is about more than taste; it’s about the presentation and overall experience. Grinding salt triggers the brain to think “this is fancy.”
I put salt in my salt shakers as well.
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(sorry, couldn’t resist)
mmm
I grew up with the Nichols damp-proof salt shakers, which was the ultimate answer to the problems of using salt. Doesn’t cake and measures out the amount. Alas, they went out of business around 1940. My grandfather bought out all he could get and sold them into the 1970s.
But salt grinders are indeed a gimmick. The size of the grains doesn’t matter all that much, since they dissolve as soon as they touch water. It’s ultimately the amount of salt, not the size of grains, that makes a difference.