There are so many reasons why PDF are a great format.
They allow almost any form of media to be inserted, from plain to text and hyperlinks, to various audio formats and even rotational 3D elements.
What's more, they can be rendered in either raster or vector, which make them fantastic for using as a base file to print from, even going so far as to incorporate fonts and effects into themselves so they're not needed as an end file.
They're also really compact. When I edited the layout for the magazine at Uni, we'd often use about 4gb on a single issue with all the hi-res graphics and what have you... the PDF file would shrink down to about 600mb, and come out from the printer's picture perfect.
They're also one of the few document types that doesn't fuck up majorly if you disk-span it across archives (useful for emailing larger files)