Before Print-on-Demand, it was impossible to think of printing one copy of a book or any other material in a cost-effective manner. Alternatives such as Offset Printing have a high set-up cost. So one needs to print a large number of copies (typically 500+) to distribute that set-up cost over all those copies. That is the only way to achieve a good per-copy cost. The whole economics of publishing, therefore, had to work on the assumption of bulk printing, with the associated operational and financial issues. But with the possibility of printing one copy at a time, thanks to POD, the printing and publishing economics can change entirely. More details about this can be found in this article on Print-on-Demand (POD).