Why bother using the book construct?

True, tags are not global within a book. But if you keep a separate template document with your tag definitions, you can import the definitions to all files in your book in one operation. With a little bit of discipline in the way you work, this will ensure consistent formatting throughout the book.

As Art said, multiple smaller files are easier to manage.
That's a polite way of saying that your losses will be smaller when (not if) Framemaker crashes...

A chapter or appendix file can be used in multiple documents.

My most common example is a Glossary of product terms that gets reused in multiple documents. It's much easier to both maintain and reuse that content when it's contained in a discrete chapter file rather than imprisoned within one or more monolithic documents...

Cheers,
RBV

Also numbering is an important issue with books. Often, the first pages of the book (a manual for instance) is numbered i, ii, iii, iv, etc. In the chapters of the book, it is often desirable to number figures and tables chapter-wise, so that it is easy for the reader to see which chapter a referenced figure belongs to, such as Figure 2-4. This latter behavior CAN be accomplished without building the publication as a book, but it is much easier and more convenient if chapters/frontmatter/appendix are different files. Lastly, the table of contents is easier to manage if it is a separate file.

In BookSpeak, a section would mean a section, which normally includes several other files or sections. But I think that you're calling a "section" and meaning a chapter.

If that's the case, the advantages would be:
* Multiple writers can be working simultaneously in different files.
* Chapters can be limited to include specific topics.
* Smaller files are more portable, easier to work on, less draining of computer resources, and easier to manage.
* Discrete files give you the ability to present different material in different ways. For instance, some files/chapters/sections may be 11x17 size drawings, but most of the others can be 8.5x11.

And, why in the world would you have different tag settings in different files, or why would you think they'd differ from file to file, or change if you didn't have access to them? The idea of using a book is to enforce a single set of styles, not to allow weirdness. The book format allows you to enforce a single set of styles effectively in all component files.

Cheers,
Art