This event fires immediately before the Plugin is unloaded or reloaded via uninstallation, Plugin/Deactivate|deactivation, or updating.

It enables a plugin to clean up after itself before its scripts stop running, e.g. to remove unnecessary instances from the DataModel. If a plugin does not clean up properly, the old copies keep running alongside the new ones, causing issues like duplicate PluginGui|guis and keybinds registering twice. When this occurs, users will be forced to close and reopen the place which is a bad user experience. It is not necessary to clean up plugin-related instances such as PluginButtons or DockWidgetPluginGuis because they will be automatically removed when the plugin is unloaded.

See also

articles/Intro to Plugins, an introductory article to plugin use and development