Why Do Recipes Call for a Sprinkle of Salt on Top?

It's just a current food fad. Someone liked the contrast of salty and sweet flavors, and it was picked up and spread through the Internet and TV cooking shows. The first time I saw this, about 2 years ago, was for homemade chocolate covered toffee with coarse salt sprinkled on top. Since then, I've seen it on brownie recipes and many others. You don't have to use the salt if it doesn't appeal to you. Not everyone likes this combination. I like it, but not enough to make a whole recipe that way.

About 40 years ago, a newspaper printed a recipe for cookies made with crushed potato chips in them! I tried it and it was cool; I've made them a few times over the years.

So the idea of combining sweet and salty flavors isn't new; plus there are other things that combine the two, like barbecue sauces, sweet-sour dishes, etc.

Salt on sweets cuts the sugar down a touch and enhances the flavor.
Adding salt to a yeast dough will stop or decelerate the rising process.