To be able to write a document on a single page, a very long page. Because when you write a mathematical demonstration and you always have to go from one page to another to see what you have written, it is not practical. Whereas if it were a single page, you would always have what you have just written above what you want to write, and not on a previous page. Digital technology makes it possible to have very long pages. It's a shame to be limited by the page length that exists in the physical world.