Details from Policy editor below:

All redirected shell folders, such as My Documents, Desktop, Start Menu, and Application Data, are available offline by default. This setting allows you to change this behavior so that redirected shell folders are not automatically available for offline use. However, users can still choose to make files and folders available offline themselves.

If you enable this setting, the users must manually select the files they wish to be made available offline.

If you disable this setting or do not configure it, redirected shell folders are automatically made available offline. All subfolders within the redirected folders are also made available offline.

Note: This setting does not prevent files from being automatically cached if the network share is configured for “Automatic Caching”, nor does it affect the availability of the “Make Available Offline” menu option in the user interface.

Note: Do not enable this setting unless you are certain that users will not need access to all of their redirected files in the event that the network or server holding the redirected files becomes unavailable.