I sometimes quilt inside the applique if I want to emphasize something like the veins of a leaf or a "dimple" in a flower. I usually outline it first to make it puffy. If it's a larger piece, such as a vase or bowl, I quilt a design inside. There are no real rules - do what looks good to you. I like appliqued parts not to look baggy and for the whole piece to have a relatively uniform amount of quilting.