Self Rising flour is a specialty of Southern baking but it's certainly nationally available and a flour homemakers used since the 50's or so (would have to check on that!). It conveniently contains salt and baking powder so a home baker could use it without adding additional salt or baking powder in a recipe. The thing is, some recipes also need baking soda which one would still have to add separately (in an acidic recipe, such as a cocoa based chocolate cake, figure on 1/2 teaspoon baking soda per cup of flour in the recipe). Self rising flour keeps a few months (and then the baking powder starts to lose its oomph).