Stevia provides sweetness with almost no bulk. It best use is in foods where only sweetness is desired, such as liquids. Eryhtritol provides bulk on par with White Sugar, so it can replace sugar in some applications where bulk is needed, such as chocolates. Its also about 70% as sweet as sugar, and thus can be used 1:1 in place of sugar [if you don't mind the food being slightly less sweet,] or mixed with a little Stevia to bring it to 100% Sweetness. Some manufacturers also make a Stevia/Erythritol Blend that is 4x as sweet as Sugar, so you would use 1/4 cup in place of 1 cup of Sugar. That would provide some bulk, though not as much as if you had used Eryhtritol on a 1:1 basis.