Today’s Question: I turned on the “Automatically write changes into XMP” checkbox [in Catalog Settings in Lightroom Classic]. Later when I wanted to exit Lightroom Classic I got a dialog telling me it was saving data to XMPs and that if I closed down it would quit but resume next time I opened Lightroom Classic. I didn’t mean to do this for the 250,000 files currently in my catalog. Is this going to increase the size needed to store all my images? What do you advise?
Tim’s Quick Answer: I recommend leaving the “Automatically write changes into XMP” checkbox turned on, primarily as an additional backup of key metadata for your photos. If you do decide to delete the files, you will need to do so manually because Lightroom Classic does not include a facility for this.
More Detail: The “Automatically write changes into XMP” checkbox in Lightroom Classic is turned off by default, but I recommend turning it on. It can be found on the Metadata tab of the Catalog Settings dialog. This will cause key metadata updates to be saved to the source image files on your hard drive, in addition to being saved in the Lightroom Classic catalog.
While enabling the XMP option doesn’t preserve all information from your Lightroom Classic catalog, it does preserve key metadata such as star ratings and keywords. Besides providing a backup of that key metadata, this option also enables you to browse those metadata updates using other software, such as Adobe Bridge.
The XMP files are quite small, taking up just kilobytes each. I would estimate that for 250,000 photos enabling the XMP option would only consume about three gigabytes. That is certainly a fair amount of storage space, but it is relatively small in the context of a typical hard drive, and I feel that consuming the additional storage space is worthwhile in terms of the benefits of saving metadata to XMP.
If you decide you don’t want to have the XMP files, you would need to delete them manually through the operating system. While this can be a bit of an inconvenience, it is safe to delete the files since the data they contain is already contained in the Lightroom Classic catalog.
Note, by the way, that it is possible to save metadata to XMP for individual photos if you prefer not to enable the option for the entire catalog. Simply select a photo (or multiple photos) in the Library module in Lightroom Classic and from the menu choose Metadata > Save Metadata to File. This will save the metadata for the selected image(s) to an XMP sidecar file, or directly to the image file for non-raw images.