Measuring cups and spoons are surprisingly inaccurate. Cups and spoons that should be the same volume often vary a lot. Worse, a lot of inaccuracy creeps into a recipe depending on what is being measured and who is doing the measurement. In our experience, the same recipe scaled multiple times can vary by as much as 10% relative to the true weight of the ingredients. This is often the reason that people find that a particular recipe "fails" when they try to reproduce it—inaccuracies have crept in at every step. Working by weight is both faster and more accurate. After a little practice you'll find yourself annoyed when a recipe doesn't list ingredients by weight.