I imagine that it can very quickly become very complicated to move even a single page, and even worse for a group of pages.
For every object on a set of pages, the links and references between those pages needs to either be maintained as to stay relative each other in the new set. Or they need to be changed, so that they keep referring to the original document. Or worse, you might want some to refer to the new doc, others to refer to the old doc.
If the object is a table, then assumptions need to be made for each and every table on whether to copy the contents of the table, or just the table structure. If there are formulas in the table, then as above, it needs to be determined how to copy those formulas.
Personally I work with a single doc as far as possible. And if there is a possibility that I (or somebody I share the doc with) will want to copy sections of the Doc, I keep everything on the same page. When the copying is done, it is then easy to organise the information into page and subpage structures.