If you don’t read a lot of cookbooks, you might not realize that there are almost as many ways of measuring flour as there are recipes. When I was growing up, my mother scooped her measuring cup into the flour canister and then leveled the top with a knife. As I started exploring more recipes, a lot of them called for spooning the flour into the measuring cup and then leveling the top with a knife. And I have even seen a few recipes that called for packing the flour into the cup, which seems like sacrilege to me! I haven’t tried any of those recipes, since it seems like there could be quite a range of packing styles, which could lead to a failed recipe if I don’t pack it like the author.
The long and short of it is, your flour measuring style could change your results when you bake. The difference between spooning the flour and packing it is several ounces or even a quarter cup. When you are baking bread it might not matter as much, since you can adjust for the flour when you are kneading the dough. But for cookies, brownies and especially cakes, it could mean the difference between a new favorite and an abject failure.
Unless I note differently in the recipe, I measure flour by first stirring the flour in the canister, spooning it into the measuring cup and leveling the top with the back of a table knife.