When I make cakes and cookies that call for brown sugar, I pack that stuff tightly into the measuring cup. I think brown sugar is awesome and it doesn’t have any negative affect on the final product.
However, the same is NOT the case for flour. When you’re measuring flour, unless the recipe specifically states otherwise, don’t pack the flour into the cup. If you do, you’ll end up with dry cakes or cookies, and no one wants that, right? Instead, just scoop the flour in there and then take a knife or other straightedge and level it off so you have a true measurement.