Austin, your response doesn't fully satisfy the question. First, while you're right that "backup" would imply that it's a backup, the word "backup" doesn't actually appear in the menu options. Some time has gone by from the original post and the original product names, but the concept of two choices still remains. They now are given as "Export…" and "Calendar Archive…" (previously it was "Export…" and "iCal Archive…").
According to other sources, "Export…" is used to export a single file, to later import to another calendar program or perhaps another computer.
"Calendar Archive…", on the other hand, is supposedly used to export ALL your calendars, and subsequently to import to a new Calendar on a different Mac (or, of course, to reload the current one). It seems to me that someone wanting to take their whole calendar environment off their office computer and get it onto a laptop or a home computer would want to use Calendar Archive rather than Export.
@Keith thanks for the great description. I am looking at this just now since I am switching over from using Google Calendar as my backend to a full iCloud solution for OSX and iOS now and I wanted to make sure I have a way to restore from a backup file all my iCloud calendar info incase I accidentally deleted an iCloud calendar, which I have found to be incredible easy to do on iOS devices.
Would you recommend this workflow to handle that?
On OS X in Calendar app File -> Export -> Calendar Archive on a monthly basis, and then if needed just grab the latest backup .icbu file and File -> Import to restore any lost event data.
Thanks for peoples' comments here.