The following points provide an overview of Omega extensions:

• Extensions serve as a set of features or a group of functionality that can be disabled or enabled as a whole.
• Extensions can provide theme settings that can be configured once an extension is enabled. The theme settings pane for the extension is only accessible if the extension is enabled.
• Once an extension is disabled the theme settings pane for that extension will not be editable anymore and all the functionality that the extension exposes will be disabled.
  Overriding whether an Omega extension is enabled or not via settings.php could be done by adding following code:

  // Disable Omega development extension
  $conf['omega_toggle_extension_development'] = FALSE;
  

• Nearly all of the core features of Omega are provided via extensions which means that Omega is an opt-in theming framework - You can enhance your subtheme by just enabling the extensions and features that you need for your use case.

Still need to add on:

Extensions: Libraries
Extensions: Development
Extensions: Compatibility