Some people wash and dry all of their fabric before using it. Starching/or sizing puts back some the stiffness in to the fabric and helps to control the fabric and prevent stretching/warping. Others just like the starch/sizing and do all of the fabric w/o washing. Others yet do not use it at all.
I do not starch everything, but I always starch my binding. This is another one of those topics where everyone is not going to agree.