Save to PDF would just give you a PDF. The idea here is that you can do whatever you like with the print-job as long as you can program it. So print to PDF is just the most simple example.

I mention a few low hanging fruits in the talk like "print to bookkeeping" - but that's just one use-case. Consider that you can use it as a printing proxy and divert jobs to different printers or implement an authentication system or a payment system before printing. There are a lot of options...