The Module Browser is an interface that displays the currently loaded and available modules in The GIMP. The checkbox, Autoload during startup, determines whether the selected module will load itself automatically when The GIMP is started. The default action is to do so.
Modules can also be unloaded. Clicking the Unload button will do this. There is, however, no benefit to be had by doing this. Once a module is unloaded, the functionality provided by the module will no longer be available to the user. To reload the module, thus providing the missing functionality, highlight the module in the listing at the top of the dialog and click Load. The module will be dynamically reloaded and immediately available.