Butter tenderizes and adds flakiness. It creates a golden-brown color and crisp textures. Butter makes cakes light and helps hold the shape of cookies.
Many people prefer butter for the taste it imparts in baking.
Either salted or unsalted butter can be used in any recipe. It is not necessary to omit or add salt. Using one or the other is sometimes a regional taste preference or choice of chefs who want to control the amount of salt in a recipe.