Search Replace Transfer
The Workflow Filters feature is intended to help you make metadata entry more consistent and allows you to identify incomplete data or other problems such as spelling errors. Run the menu command under Plug-in Extras > Refresh Workflow Filters and the plugin populates a range of fields which can be shown in the Library Filter panel or used in Smart Collections:
All of these extra fields can be shown in the Filter Panel (below) or in Smart Collections. Here in the Library Filter Panel, #Keywords shows me that 2 images have no keywords assigned, while most others have 6-10 or 11-15. So those 2 images probably need more attention.
Refresh Workflow Filters
Note that these columns do not show “live” values - they have to be recalculated each time you run the Refresh Workflow Filters menu command.
You can do this using the menus, or you may want to set up a third party keyboard shortcut app to do it.
This need to recalculate has a useful effect on how you might use Smart Collections:
Extra Workflow Filters 1-5
You can define up to 5 extra fields to recalculate with the Refresh Workflow Filters command. This means filter the library by almost any field including EXIF, IPTC or Develop values.
The extra fields are set up in Plugin Manager: