FTP is used in some printing environments to transfer a print job to a server, where it is then printed. The IETF (Internet Engineering Task Force) discusses issues of FTP printing as far back as RFC 448, "Print files in FTP". The article discusses files with unknown format (probably binary), plain text files. and ASA formatted files.
HP offers FTP printing in some of their JetDirect print servers. We found an article Scanning and sending via SMB/FTP which describes setup.
We also found a security article that suggests that using anonymous FTP (that is, no login or password required) to transfer files may result in printer abuse. We have heard the same concern from clients in the industry as well. If your print server offers FTP printing it may be worth asking the vendor about optional login support.
Based on our own experience, we recommend that you never setup an anonymous FTP server outside of your network security. We did this once in the late nineties. Within 5 minutes, it had already been hacked and we had to take it down.