This would be a useful feature for the following reasons:

eg you have just finished working on PROJECT-No-1, which was a 6 year project with (for example) 2,200 items in JIRA, and you decise to just archive it. It would be nice if you could just "export" PROJECT-No-1 and save it somewhere.

eg six months later, there is an audit on your prior project called PROJECT-No-1. You therefore now need to see all the items that are in the PROJECT-No-1 archive file located on your hard-drive. It would therefore be necessary to be able to "import" the archive file back into JIRA, so that you can review / audit historical items in JIRA.

etc, etc