Instead of printing directly to a printer, you can print to a file.
Then you can transport that file to somewhere else and use an old DOS command to
copy that file to a like printer.
If your printer is a generic text printer, it's a lot like File|SaveAs using
"save as type:" Formatted Text (space delimited)(*.prn).
But if your printer is anything else--laserjet, inkjet--anything that needs
special codes, then this file that's created is unreadable by humans--and it's
only useful if you copy it to a like printer.
A lot of printers won't speak other printer languages--that's why you have to
have different printer drivers for each make (and model) of printer.
Why would someone print to one of these files? My guess is that it's useful if
you want to create a PDF file. Sometimes you have to print to a postscript file
and have that postscript file get translated (distilled) into a .pdf file.
A lot of applications can do this. If you have a nicer printer at work (say)
and you don't have the application there, you could load the printer driver on
your home pc, print to a file, and then take that file to work and print it
there.
(I bet not many people do this, though.)