In the architectural world we often have recognisable drawing sets, for example, for concept stage, planning stage, detail stage, construction stage, etc.
It often makes sense to have a single Layout file that gets added to as projects pass through the stages, not least because some drawings may need to appear in more than one set.
It might be useful to have a tagging system for the pages in Layout. That would make it easy to filter them for a particular stage making output easier. Tagging is better than a hierarchical system because any one element can have more than one tag.