It is key to see the interactive model to answer this question. I don't see any limitations when I first saw the model or when I revisited it. In science, relative size is a clue that helps a person figure out how close objects are to the known size of another object. This isn't always accurate, because all humans have faulty judgments at time. We do use this concept in many fields, including science, to determine the size of planets.
It can also be used in real life situations. For example, if we know a shoe is size 8, and there is another shoe that is smaller in size, but the size is unknown, we can guess that the size is 7 because it is slightly smaller than size 8.