Today’s Question: For Lightroom Classic, would it be OK to just back up the catalog and not the previews? My previews take forever to back up.
Tim’s Quick Answer: Yes, it is perfectly safe to exclude the previews from a catalog backup for Lightroom Classic. In fact, the built-in backup feature that I recommend using automatically excludes previews from the backup.
More Detail: I strongly recommend backing up your Lightroom Classic catalog to help ensure you are safeguarding the information about your photos. Obviously, you should also be backing up the photos themselves as part of your overall backup workflow.
There is no need to back up the previews that are included in the folder along with the actual Lightroom Classic catalog, because those previews can easily be re-built later should you need to recover from a backup of your catalog.
Even if you are backing up your Lightroom Classic catalog using other software, I still recommend using the built-in backup feature to back up the catalog on a somewhat regular basis. That is because the built-in backup includes options to check the catalog for errors and to optimize the catalog. I recommend making sure both checkboxes for these features are turned on in the dialog that appears when a catalog backup is initiated.