Drupal menu structure

The structure of Web style portion of the site is based on the primary links option. The navigation menu is primarily concerned with content management and administration, and can in fact be hidden from anonymous (casual) users, while the secondary links can (probably?) be ignored for the purposes of this discussion.
As new pages (nodes in Drupal terms) are added they are given a menu title and located in the menu structure. The image below combines the menu (user view) with the underlying admin view to show the correspondence between the visible menu structure and the primary links. The Drupal menu structure is very flexible, nodes can be dragged both up and down, as well as left to right, to change their position, and relative importance within the menu.

It is perhaps tempting to think that this menu structure is fixed. It isn't, unless of course you plan the site to be static. As new material is added it may be necessary to split a section up, or introduce a new level of detail in the hierarchy. It is not possible to predict in advance, how the menu structure will evolve.
The structure is determined by the author(s), however give two people the same material to organise, and its unlikely they will come up with exactly the same solution, especially as the number of pages (nodes) grows. Even the site author can lose a page, or forget the reason it was placed where it is, therefore another method of locating the page is needed, either using the taxonomy or search facilities provided by Drupal
Another problem with any menu structure, is that a page may fit equally well in two or more separate positions within the hierarchy. Do you

• duplicate the page, and remember(?) to keep them both updated, or
• Cross link them, either with a hypertext link, or using the taxonomy keyword(s)?

For example a page explaining hexadecimal numbers will fit under HTML when explaining RGB colours. It also fits under networking when discussing subnet masks. You don't need to know what this means, just that they would be two distinctly different nodes in a menu structure