No it's not a common workflow. Like I said: a backup is a copy. A backup of your current catalog should be an exact copy of your current catalog. If you use a backup application to backup the entire catalog folder (so also the previews), you will find that this goes quickly and efficiently. The application will only backup new previews.
Lightroom can also make backups of your catalog on quitting the program, with the option to verify the integrity. In this case you only get a copy of the catalog file, though. The previews are not backed up, because previews can be rebuild.
The system you use now is unneccesarily complicated. It's also a bit risky. Because you work with this backup catalog (you open it in Lightroom and import stuff into it), you have no certainty that this backup could not become corrupted at some point (unless you regularly run an integrity check on it).