Samuel Pepys writes in his Diary that he had been at the booksellers buying books and specifying how they were to be bound, or getting his old books rebound in a uniform style. At that time it was the general practice that booksellers held stocks of books in unbound sheets as delivered by the printer, and that the purchaser would commission a binding to suit his taste and pocket.
Since the mechanisation of paper-making in the early nineteenth century, books are machine-bound by the thousand. When a modern binding falls apart, it may be cheaper to buy another or to find a better copy in the second-hand or antiquarian book market. On the other hand, it may have value over and above its recommended retail price. It might be scarce, or it may have some powerful association attached to it, and therefore be worth repairing or rebinding.
The basic function of a binding is to protect the text, but may be and often is a significant artefact in its own right. Repair may range from a simple tidy-up, to a re-back process, or possibly, a new binding. Good conservation practice requires intervention to be as little as possible, so the best approach might be to leave it alone and make a box to keep it in. Each book needs to be assessed, and the work to be done determined.
(file: 744Bookbindings.pdf text:Illustrations of books bound or rebound or repaired - PDF )