I rarely use the book feature, preferring to keep all the contents of a publication in a single ID file.
Document is what you want. A book file is nothing more than a way to organize and synchronize a group of documents. It allows them to easily share styles, numbering, swatches and master pages.
Like this: I'm staring a catalog, and each section of it is in a separate document. As I create them, I add them to the catalog book so I can keep numbering and styles consistent. All the documents in the book file can be output together into a single PDF for printing.
If you book is long, you can break it up this way to keep it from becoming too unwieldy.
Thanks, Mike—selecting book looked weird.
As mentioned above, Book is a repository of ID filenames and is useful in the situation described (separate publicaitons to be synced for styles, numbering, etc,). But in and of itself it is only a tool for those purposes.
I have used it in similar circumstances. But only if/when I feel the shear number of images would otherwise bog down ID. Which in my case isn't very often.