Hotmelt dries nearly instantaneously So it is also cheaper then cold glue In a time that asks for speed and competition, this is a great benefit. But it has its downsides too, which is why PUR was brought in. PUR glues just about everything for life. Regular hotmelt is a thick layer
Glue is a common good in book binding It is used to structure the spine of a book You need glue to attach the cover to the spine for a paper back The end sheets of a hard cover book are glued to the cover This has been so since the first book was bound
Cold glue is the most ancient of glues. It used to be made of water mixed with animal bones ground to powder. Without this substance we would not have had any books. And its purposes are manifold. I think it is an underestimated contribution to civilization. The biggest benefit is that it creates no stiffness.