If you are american, I’m sure you’re not a fan of the metric system, but you should be able to understand why cups are not always the best measurement. Growing up in Europe, I’ve come to used to using a scale, mainly when it’s most important, depending on the recipe and the ingredient.
Before you jump to conclusions, I dare say that conversion methods on the internet are not reliable, if you diy with wichever ingredient of your liking, notice that it doesn’t always give the same result. Imagine a tablespoon of baking powder, about 15 g (conversions say), but we human beings are not so precise to replicate the exact tablespoon, over and over again. Say one day, instead of the 15 grams, you get 18 (from the same spoon) that is 20% more leavening agent you got, compared to what you need! So the upcoming result will not be the same, and there goes another lava exploding cake to dirty the oven. And ruin your dessert. And there you go again to bake yet another faulty cake.
In the professional world, weighing is a must, if you don’t give a flip, and only bake occasionally, then by all means, imperial system is your best friend. Please note that you should always go by the recipe, do not attempt conversions, unless you want to try to make your own table of measurments, in case of a rainy day when your skale’s battery needs replacement. And you don’t feel like going out to buy a new one.
Above all, be precise in any baking recipe, I don’t follow amounts for cooked meals as it’s all about improvising and trusting taste buds.
Mel's Vittles 
I love the shows on American cable where they explain the chemistry of cooking. It isn’t stuff you necessarily have to commit to memory, but gives one an understanding of how the ingredients actually work to create the dish. I really loved watching Alton Brown’s Good Eats for that knowledge. It demonstrates the need to do more weighing and less “cupping” for precision. With some recipes and ingredients a 10% variance is the key to failure.
Yes, I agree. In pastry classes we had to use scales for everything – it is fundamental for assuring the cohesiveness and recurrence of a recipe. When asked why we couldn’t use volumetric measures (1 cup = 240 ml = 0,24 L) the answer was: the ingredient might be compressed, which will alter weight in a determined space. For ice cream making for example, this is utterly important. In Portugal we don’t get many shows that go on American cable, some on food network, but mostly Guy Fiery and Ina Garten – not much imperial vs metric explanations there! I will surely look into Alton Brown – thank you for that.
Great post and I agree about weighing being better. Some of us would love the US to go metric! Hoping this happens in my lifetime.
I hope so too! I must say – I use both methods. Basically for anything requiring scientific phenomena – metric. When I cook my heart out with any savory dishes that don’t require much detail, and ravishes in plenty improvisation, I ditch both methods and rule my cooking according to taste.