Binding is the part of a book that nobody admires and everybody notices the moment it fails.

Pages folded into sections and sewn through the fold give a book that opens flat and stays together. It costs more and takes longer, and for anything meant to be used — a cookbook, a reference, a score — it is usually worth the argument with the budget.
Pages are milled flat at the spine and glued. It is cheap, fast and perfectly adequate for a paperback that will be read once. The weakness is predictable: a thick book bound this way will not lie open, and a reader forcing it flat is slowly destroying it.
Whatever the binding, part of the inner margin disappears into the spine, and how much depends on the method and the bulk of the paper. Designing a generous gutter is not wasted space — it is the difference between a reader holding the book comfortably and fighting it.
Ask the printer for a dummy in the actual stock before the layout is final. It answers questions that no amount of screen proofing will.
A hardback fails at the hinge long before the sewing gives out. The joint between board and spine takes every opening, and the material choice there — cloth weight, how far the covering turns in — determines whether the book still works after a few hundred uses. It is also the detail most often decided by cost alone, because it is invisible in the sample.