Using a scale to weigh your food is much more accurate than using measuring utensils such as cups and spoons.
Factors such as under or overfilling measuring cups and spoons, the variation in density within certain products, and air pockets that form when scooping out dry goods can really throw off the accuracy of measurements when you use measuring cups and spoons to determine serving sizes.
Consider the following real-world examples:
½ cup of dry oatmeal can result in anywhere from 30-60 grams of oats being used. That is a difference of 50 - 100 calories, which can easily throw you off for the day.
A true tablespoon of peanut butter weighs about 16 grams, but it’s super easy to pile on just a little extra, which can add around 20% more calories to your serving.