The other excellent use for ice cream salt is to sprinkle it on concrete steps and sidewalks, to keep them from freezing.
But it's also essential for freezing homemade ice cream, and it takes someone who knows how to freeze ice cream to get the proportion of ice and salt exactly right, to keep the ice cream soft and not grainy.
I don't have that knack, but my dad sure did. He knew exactly when to add ice cream salt and when to add ice. He also knew how much to add. It's a very fine line, but he knew how to do it.