Well, I've now gone several miles down each road. I've used both the many-files InDesign "book" feature and the single-file feature for many weeks each, and I have a definitive answer:
I can't envision ever using the InDesign "book" feature again. Ever.
The manuscript I'm working with contains just under 300 pages, logically organized into 100 small chapters. When I started the project, I organized the book physically into a single document. Life was mostly OK, but the following "book" features sounded nice:
- I wanted chapter numbers (not just titles, but numbers and titles) in my running headers. A book makes chapter numbers accessible to the running header mechanism.
- Master management would be much easier. Using a book, the first page of each separate file uses a master with folio but no header, and subsequent pages use a master with both a folio and a header. With a single file, I had to manually move masters around whenever I wanted to export to a reviewer, every time I changed the page count.
- And kind of a minor bonus, maybe a book would make it easier to re-order chapters during the phase where I was still learning how best to logically arrange the content.
These features were alluring enough to me that I decided to change my manuscript's physical organization. I spent several hours over the course of a couple days meticulously separating my single-file manuscript into 100+ separate "book" documents. What followed was a hellish experience. Here's why:
- Style synchronization is really inconvenient. I'm intimate with how it works, but still, I can't count how many times I'd make a minor tweak to a style and then five minutes later—after tweaking a style in another file too—realize that I hadn't made either tweak to the sync master. ...And then try to remember which two of the hundred files I just changed.
- The simplest things, operations that you expect to execute instantaneously, became ridiculous. To perform a global find and replace, for example, requires you to have all 100+ files open at once. Working with 100+ tabs open is preposterously hard to do. Just closing them all takes several minutes, requiring several clicks per tab. Opening so many files obliterates the utility of File › Open Recent. Even having 100+ files in the Book panel was difficult, because with so many files in the list, there was no space left to click into to de-select all files. The feature was clearly not designed for using so many files. The "book" feature just creates extra friction pretty much everywhere you look.
- Overview visibility is impossible without exporting to PDF and viewing the overall document there. This, by the way, is the workaround for the global find problem. I was doing find operations in my PDF viewer instead of within InDesign. Regular expression searches? Hope you don't need 'em.
- Table of contents generation and updating is buggy, complicated, and slow. Generating an accurate TOC would sometimes take me in excess of 10 minutes and several tries. One particularly annoying feature was that updating a TOC would first delete the existing TOC, which would collapse all the now-empty pages, which would then create an overset text problem, requiring me to manually insert the pages back in. I found a workaround for this: I put an empty text frame on each page, which counts as "content," so InDesign would not collapse the pages.
- Fixing overset text problems caused by section titles confined to start on the recto would waste more than 15 minutes of manually inserting blank pages into my section head documents, every time I wanted to export after having changed my page count.
- When I used the "book" feature, InDesign would crash incessantly. Many workdays, I would send 10+ crash reports to Adobe. Some features (attempting to export to IDML, for example) would guarantee a crash every time.
- The final straw was trying to index my manuscript. I never completely figured out what was going on, but apparently you can't build a proper index without having all 100+ files open at a time, which was simply not something I was willing to try a second time.
So, I invested the hours it took to reassemble everything back into a single "big" file (it's not really that big), and I'm loving life again:
- No more synchronizations to mess with.
- Everything is quick and responsive.
- It's rare now to have more than one InDesign crash in a day.
- Moving a chapter from here to there wasn't ever really that hard; it's just a cut and paste.
- TOC updates are accurate and lightning fast.
- Indexing is fast and easy.
- I can put a chapter number in a running header if I really want to (https://www.youtube.com/watch?v=sBgBQJLErCM), but since my chapters are so short, I don't really need to.
- There's no need to manually adjust any of the section title pages that are directed to "start paragraph on next odd page".
When I converted back to the single document, though, I still had the problem of needing to manually manipulate which master is assigned to each page, which changes when I change my page count. However, my question at How can I automate Apply Master and Start Section selections? contained an answer that I found compelling. After some research, I purchased the tool called "Mastermatic" from https://www.id-extras.com/. It allows me to define rules like, "When a page has a Chapter Title, assign it the 'B-Master +Folio -Head' master page." It's a good solution for my final problem with using the single-file feature. (I am not affiliated with id-extras in any way.)
The clear answer for me is to not use the "book" feature. I've used it, and I can't imagine any scenario in which I would ever try it again. My experience with it was uniformly infuriating. I'm able to do everything I need with my manuscript organized as a single document.