PgMetadata is made for people using QGIS as their main GIS application, and PostgreSQL as their main vector data storage.

The layers metadata are stored inside your PostgreSQL database, in a dedicated schema. Classical fields are supported, such as the title, description, categories, themes, links, and the spatial properties of your data.

PgMetadata is not designed as a catalog application which lets you search among datasets and then download the data. It is designed to ease the use of the metadata inside QGIS, allowing to search for a data and open the corresponding layer, or to view the metadata of the already loaded PostgreSQL layers.

By storing the metadata of the vector and raster tables inside the database:

QGIS can read the metadata easily by using the layer PostgreSQL connection: a dock panel shows the metadata for the active layer when the plugin detects metadata exists for this QGIS layer.
QGIS can run SQL queries: you can use the QGIS locator search bar to search for a layer, and load it easily in your project.

The administrator in charge of editing the metadata will also benefit from the PostgreSQL storage:

PostgreSQL/PostGIS functions are used to automatically update some fields based on the table data (the layer extent, geometry type, feature count, projection, etc.).
The metadata is saved with your data anytime you backup the database
You do not need to share XML files across the network or install a new catalog application to manage your metadata and allow the users to get it.

And the plugin contains some processing algorithms to help the administrator.