First you have to know what the space-filling model is. The space-filling model is a model used to show the structure of the atoms. It specially shows the relative sizes of the atoms and how the space between atoms (inside the molecule) is filled. It does not show the angles and lengths of the bonds. So, the disadvantage of using a space-filling model to show a chemical compound is that it will not permit to observe neither the angles nor the lengths of the bonds in the molecule.
