It saves the binder from writing out the name of each volume on his bill, and as the librarian must keep a list of books sent, why not keep them this way as well as any other?
I have mislaid or lost hundreds of lettering slips, which are the bane of a bookbinder's existence.

Lay down some rules for the cutting of books, placing of plates, binding of covers, and advertisements, style of lettering, etc., and have your binder follow them.
Don't ever cut with a folder before sending to binder, as it makes the sewing more difficult.
Don't pull to pieces or take out titles and indexes.

The binder always takes care of that.
Don't take off ads, as it sometimes leaves unsightly tears or takes away pages, and if all leaves are paged the binder is at a loss to know if the book is complete.
Don't ever use mucilage or glue.

Your bookbinder will send you a little paste, or you can make it by boiling flour and water and sprinkling in a little salt.

If you wish to keep it for a long time, mix a few drops of oil of cloves with it and seal up.
Of course there are cases where some of these rules don't apply, such as volumes made up from leaves taken from several other volumes or pamphlets.
In case of a book of this kind place every leaf in correct order, and write directions very carefully." Many books will need repair.