Today a lot of sheet music comes straight from the composers hand (or, more likely typeset with computer programs such as Sibelius, LilyPond or Finale), and is published or presented to performers without the layout having been professionally designed by engravers or autographers. This book can be of great help to the composer or orchestrator who typesets his own music for performers, and may contribute to avoiding future publications of ugly computer generated sheet music which is increasingly presented to performers and conductors.
Some of the content in the book is outdated and irrelevant to us today (though is a very interesting historical presentation of the traditions of producing sheet music), but there is so much other priceless information that is difficult to find anywhere today, and is a real wake-up call as you realize that many of the decisions taken by digital typesetting programs are not necessarily optimal for producing the best result, as there are many exceptions to the rules that these programs by default follow.