Halacha is not only formal laws, but also a way of life more generally. The Mitzvah of Bracha frames our meals, and thereby also guides us in proper social dynamics of eating. This includes good character traits, but as a social institution also the manifestation and appearance of those traits. Thus, for example, one shouldn’t distribute overly large or small portions since it looks like an expression of a bad character trait (with too small appearing stingy, and too large appearing gluttonous) (7:3).
One key goal is not embarrassing a host. Since we live in a social world, we must take into account all social dynamics, going so far as to take into account potential future misunderstandings which could lead to his embarrassment, even if your action is benign. His specific example (7:10) is not sending wine with a layer of oil on top (to preserve it), since that could lead him to believe that a future gift of oil is wine leading to embarrassment when guests come and he doesn’t have wine. Changing the meaning of a barrel with oil on top is a negative externality we must attend to and avoid.