The reason you'd use a salt grinder is when you specifically want an inconsistent spread of grain sizes in one single application. Like salt flakes on ganache o

The reason you'd use a salt grinder is when you specifically want an inconsistent spread of grain sizes in one single application. Like salt flakes on ganache or caramel, or there's a beloved french butter with large crystals mixed into it. 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.