Today’s Question: I just noticed the “Purge Unused Keywords” on the Metadata menu in Lightroom Classic. How would you have any unused keywords in the first place, since they are created by being added to a photo? Do you recommend using this command?
Tim’s Quick Answer: Unused keywords would result from either removing a particular keyword from all photos it had been assigned to or importing keywords that you haven’t yet assigned to any photos. As long as you don’t use a controlled vocabulary in your workflow, I would generally consider it safe to purge unused keywords from Lightroom Classic to reduce clutter on the Keyword List.
More Detail: When you add a keyword to a photo in Lightroom Classic, that keyword will be added to the Keyword List if it wasn’t already on the list. In addition, it is possible to import keywords from a “controlled vocabulary”, so that you can pick and choose keywords without having to type them in yourself. In either case, you can populate the list of keywords on the Keyword List found on the right panel in the Library module in Lightroom Classic.
You can, of course, also remove keywords from photos. If you remove a given keyword from every photo it had been assigned to, that keyword will obviously then not be assigned to any images in your catalog. That would represent an unused keyword.
Similarly, if you import a keyword list (by choosing Metadata > Import Keywords from the menu) you will find all of those imported keywords on the Keyword List. It is quite possible to import a large number of keywords that you never end up adding to any photos, which again would result in unused keywords.
On the Metadata menu, as noted in today’s question, you can find a “Purge Unused Keywords” command. If you issue this command, any keywords on the Keyword List that have not been assigned to any photo will be removed from the list. Note that on the Keyword List the number to the right of each keyword indicates how many photos that keyword has been assigned to.
If you have unused keywords because you removed keywords from some photos, you may very well want to purge those keywords from the list. If you have imported a keyword list as a controlled vocabulary, you may not want to purge unused keywords, because you may eventually put some of those keywords to use.
Note, by the way, that it is also possible to delete individual keywords from the Keyword List by right-clicking on a keyword and choosing Delete from the popup menu. Keep in mind that deleting a keyword from the Keyword List will also cause that keyword to be removed from metadata for any photos to which the keyword has been assigned.