The Sandbox allows you to edit documents in the oXygen editor when you are away from a network connection.
You can also use the offline mode to enable Nomadic editing. This feature supports working on a document when no internet connection is available. For example, you can work on your laptop while traveling on an airplane and don't want to pay excessive connection fees.
Once a document from the repository is stored in the Sandbox, you can save it and end your editing session and exit the oXygen editor and Astoria. Later, you can launch the oXygen editor and open the file from the Sandbox and continue editing and saving the document, but features that depend on network access to the repository are disabled. The document remains checked out to you and locked. When you again have a network connection available to the repository, you can log into the Workbench, launch the oXygen editor, open the checked out document, then check it into the repository. The copy of the file is removed from the Sandbox.
Keep in mind that when you have repository objects checked out and saved in your Sandbox folder, they are locked in the repository and cannot be modified by other users until you check them back in.