For all format printing, although you might create and archive artwork in its originating application in its “native” format such as PSD, AI, etc., you might also want to save a copy of the file to send to a client or offsite for output.
The Save As option in the File menu allows you to save a copy of the file in one of the standard formats. Save As also allows you to rename the file, flatten layers, simplify artwork, reduce the file size, and remove any extras such as annotations, paths, etc