Function
Functionality of all-purpose flour is determined by several factors, such as:

Ratio of hard wheat: soft wheat and the protein content of the flour
Bleaching or maturing
Flour that is freshly milled or ‘green’ does not make doughs and bread with proper rheology and texture. So, there’s the need for aging or bleaching. This step is beneficial in terms of:

Oxidizing the sulfhydryl groups of the protein, thus improving dough elasticity
Whitening the flour
Improving the baking characteristics.
Application
Bread
Cakes and muffins
Cookies
Noodles
Pancake and pastries
Pizza and pie crusts
It should be noted that cakes made of this type of flour are typically not as light or tender as cakes made out of cake flour. Similarly, bread made with all-purpose flour tends to be softer than that made of bread flour.

All-purpose flour can also be combined with other types of flour such as durum to produce semolina bread, whole wheat flour to produce whole wheat bread, or soybeans to produce spaghetti.