The spine says it all
During your book's lifetime in a bookstore, it will probably present itself to the prospective buyer by the spine alone. Very few books are given the shelf space it takes for a "face out" display. After purchase, your book's life on a bookshelf will show the spine almost exclusively.
Books with fewer than 64 pages are too thin (unless heavier paper is used to "bulk" up the thickness) to support a spine. Instead, small books are saddle-stitched (stapled) or spiral bound. Many bookstore managers do not consider a stapled book to to be a "real" book. A library may classify a stapled book as a "pamphlet" or "brochure."
Spiral binding, whether plastic or metal, also gives book managers the shudders. For one thing, they tell us, the books ship badly. Scratching and crunching are common. For another, they display poorly on the shelf, although some kinds of plastic spiral bindings allow for an imprint on the spine. The third problem with spiral binding is their life expectancy. At every puncture point the paper of the book is subject to additional wear and tear. Having said that, I must add that printers with a good track record of providing quality plastic and metal spiral bindings know how to minimize the problems. Spiral or "O" ring binding remains popular especially for recipe books, manuals, and other guides.
Dimensions
The thickness of your book depends on the number of pages in the book and the "weight" or thickness of the paper used. A book using 60 pound text paper will probably run about 444 numbered pages per inch. (That's 222 sheets of paper, printed both sides.) So your 192-page book will be approximately 3/8 inches thick. Today's glue and binding techniques will hold your book with up to three inches thickness and more without cracking or breaking when it is opened.
Designing the spine
Your cover designer will include the spine in the artwork for your cover. A good designer will sure that the tiny bit of space available on your book's spine is being used to maximum advantage. As a rule of thumb, the main title, author's name, and publishing firm appear on the spine. Even better if art from the cover can be repeated or continued on the spine. Insist on a title that is readable from 5 to 10 feet away. Reverse type (white on a color), italics, and fancy lettering may only end up making the spine harder to read.