CUPS adds basic support for 3D printers.
“Added support for 3D printers (basic types only, no built-in filters) based on PWG white paper.”
http://www.cups.org/blog.php?L1087
The PWG Whitepaper is at http://ftp.pwg.org/pub/pwg/BOFs/3d-printing/wd-apple-ipp3d-20150413-rev.pdf
I have added a link to the Whitepaper that describes the functionality.
It looks like this is for printers that use s3g binary instead of G-code. Basically just TakerBot, their clones and the handful of folks running Sailfish otherwise. The only benefit I see in having CUPS support is to make the printer a shared resource across a LAN.