Three different models have been demonstrated which allow to define in a structure if a hydrogen bond is present or not. In many cases dealing with protein structures this models might not be the first choice, as the positions of the hydrogen atoms are not known. For practical use it is also often easier to use a simple distance or angle cut off.
The aim of the assignment was therfore mainly to show, that there exist a lot of weak interactions or bonds we normally ignore and it may be necessary in future to focus more on them.
The bond valence model, which allows to quantify even weak interactions, gives us a tool to decide, what or how much we ignore if we neglect these weak interactions.
My belief is, that the understanding of weak or 'non-bonded' interaction will play a mayor role in our understanding how proteins work. I hope I have contributed a tiny bit to this understanding.
People who are interested in more depth about this topic may mail me