I used to disdain the differences between types of flours. But as I got more interested in good baking, and became more concerned about not wasting ingredients (=money), I am forced to admit that you do need to use the proper flour for different kinds of baking.
So, there is bread flour for bread baking. Pastry flour for pastry-making. Cake flour for cake-making. The great Shirley Corriher uses self-rising flour for biscuits. And so on.
What is AP flour good for? What's left? Thickening gravies, I guess, but does that justify buying a 5 pound bag?