First of all, this is just my imagine.
If we can exporte b2 online articles to backup files, it may facilitate in the use of following aspects:

1. Offline Reading
Exported documents which are beneficial to read. (such as txt, word or html). It's convenient for storing on local hard disk or U disk, reading in an environment without network.
2. Backup and Import
Exported documents which have the support of importing (such as xml or cvs). As backup, on one hand, it can recover accidentally deleted files; on the other hand, it is easy to move or import some articles to other blogs.