Most people probably won't use a food scale, but if one needs a food scale, it's most likely because you need to measure the amount of food you're going to eat so that you don't over eat. I know people on diets use them.
A food scale can be a useful tool for a person trying to lose weight or stick to any other strict diet. Many foods label servings in ounces so a scale makes it easiest to ensure the correct serving size.