For me it is very useful as I haven't had any education making costumes and there are a lot of sewing techniques that I need explained.
Also I really love the fact that my grandmother probably used this book when she learned making costumes as well as she was a seamstress.
Besides sewing techniques there is also a lot of information about what was appropriated to wear when. For example it tells the difference between morning wear, day wear and evening wear but also between mourning wear.
I really recommend this book to all Dutch seamstresses especially if you want to make Victorian and Edwardian clothing.