(Excerpt from one of my tutorials)
Backups taken by LrC when you exit the program are not required – until they are. The question of how long to keep them keeps coming up. The answer depends on several things such as how much disk space you have for such things. However, some basic principles apply.
DIMINISHING VALUE OF OLDER CATALOGS
To be used as a full catalog restore in case of a complete loss or corruption of your primary catalog, the older the backup is, the less useful it becomes. This is due to:
The farther back in time you have to go, the harder it is to recall everything you’d done since then.
The farther back in time you go the more work you’ll have to do to replicate what you did in LrC since that backup was taken.
Most (but not all) problems that might require a full catalog restore (like catalog corruption, failed drive, stolen computer, Etc.) become obvious rather quickly. However, some don’t make themselves known for quite some time.
If you did any folder or image file moving, renaming, deletions, or other “physical” changes after the point the backup was taken the recovered catalog won’t know about those changes and untangling that can be quite challenging.
This is why I recommend creating a catalog backup every day where you do something in LrC. But,in general the older those backups get the less likely it is that you’ll want to revert to one of them rather than keeping your current catalog and fixing whatever it is that went wrong (if you can).
LONG TERM VALUE OF HAVING OLDER CATALOGS
Sometimes you want to just “see” what something looked like from a long ago point in time or need to recover data for just some images from an older catalog. For example, you accidentally removed a folder or collection and need to get those images, with their edits, back. Another example is for technical reasons you have to go back to an older version of LrC which required an older catalog format.
For these situations having catalogs that go back farther in time are quite useful. In general these ‘older’ catalogs are used as the source for an “Import from another catalog” where you select only specific sets of images rather than reverting to the entire catalog.
A SUGGESTED BACKUP RETENTION PLAN
Create a new backup folder for each new version of LrC that requires a catalog update so you can easily know which version of LrC the backup is for without having to drill down, one by one, to the zip file name. This was less important, prior to LrC 14.0 when LrC was appending version numbers to the end of upgraded catalog names but I still found it useful even then. Since LrC is no longer including the upgraded version number in the catalog name at all so using folders for this even more useful.
Set the LrC Preference to create a backup every time Lightroom exits. Then actually take a backup at the end of any day in which you made any changes in LrC. I suggest shutting down LrC at the end of each day and that’s when I have it do the backup. This also lessens the risk of damage due to an overnight power failure or power spike.
Set LrC to store the backups it creates upon exit on a drive which is not in the same housing (box) as where the actual catalog is.
If you’ve done any major folder structural changes or file renames other than imports in that session make some sort of note on the backup Zip file name or keep a log of major structural changes
Retention Schedule:
Keep all of these backups for 90 days
For backupups taken in the 2 years before that, keep the first one from each month
For backups older than that keep 1 to 4 per year (say first one of each year or quarter)
The retention durations above are just what I use. Feel free to pick different duration spans as desired. Many people use 30 or 60 days, and 1 year