As mentioned in the Creating a master library from the Data model viewer recipe, a great benefit of creating a master library is to save you time and reduce the complexity by applying global changes to your visualizations.
There are three main areas in the asset panel when editing a Qlik Sense sheet (Charts, Custom objects, Master items, and Fields). Clicking the chain button () opens the Master items pane.
From here, you can manage every aspect of the Master items, such as renaming, replacing, deleting, and editing.