The Preload Reference Editor is used when you want to select specific file references to be loaded or unloaded when the scene is opened.
To selectively load file and proxy references using the Preload Reference Editor
The file browser appears, listing the default scene directory for your project.
The Preload Reference Editor appears. The Preload Reference Editor lists all available file references for the scene. Depending on how the Referencing options were set, some file references will appear loaded or unloaded in the Preload Reference Editor. When an icon appears beside a particular file reference it indicates that one or more proxy references exist for that reference.
It is possible to set the load or active state for multiple proxies simultaneously when using the Preload Reference Editor. The list of proxy tags that appear in Set Active Proxy To submenu (when multiple file references are selected) is generated from all of the proxy tags currently in use for the proxy sets associated with the selected file references.
Loading and unloading references works hierarchically; that is, switching the top-level load status of a parent to unloaded means that all child references are also not loaded.