Metadata is information about files and is used to link compatible assets together, like linking compatible textures to clothing assets. Daz Studio uses metadata to categorize compatible user-facing files. For example, there is no way to know if a file named “Crazyheart.duf” is a character or a pose or what it works with. Its name is not an indication of what it contains. But by using the content_management_service to assign information (metadata) about each file, that information can be displayed. After assigning metadata to “Crazyheart.duf” to determine its name, category, etc., Daz Studio displays it as a materials_preset for a cartoon-style horse.
Metadata is important because the Daz Studio 4.x Smart Content pane only find files that have metadata assigned to them. All of the products in the Daz 3D store will eventually have metadata. Products or files from another source that do not provide metadata do not appear in the Smart Content Pane (Tab) but do appear in the Content Library pane. Add personalized metadata by using the Content DB Editor... action. Also products from the Daz 3D store prior to those products having assigned metadata will include an easy way to update the metadata for those products when metadata becomes available.