Having the same pages or subpages included in multiple documents as pages, subpages, or snippets. This would allow you to have a single source of truth for a document and have it directly accessible in multiple documents.
Use case:
I have a sprint folder where for each sprint I create a document with certain information and notes etc. I want to add these docs as subpages or snippets in a "master" document, e.g. on the folder level or even in a different space.