Query about structured Frame templates

In Frame 12 all the templates have been updated.

I built my book using unstructured templates because I wanted to get a feel for the changes from my last version of Frame (8).

I now think I will need to redo the book entirely using the templates from structured Frame.

The unstructured Frame template for a book has all master pages in every file in the book. The structured template for Chapter has only master pages: left, right, first. Is there a reason for this? (Should not every file in the book have the same master and reference pages?)

Thanks.