Paperless offices, innit.
Also means you can generate PDF's from other formats easily, without needing to create the PDF in a PDF writer to start with - you just click "print" on the application you are using (be it a word processor or spreadsheet) and you'll have a nice PDF to email, instead of either printing and mailing/passing around, or depending on your recepients having the same software. It also means the document is "permanent" (well, more permanent than a .doc or whatever)