This policy setting allows administrators to disable all trusted locations in the 2013 versions of the specified applications. ...

This policy setting allows administrators to disable all trusted locations in the 2013 versions of the specified applications. Trusted locations specified in the Trust Center are used to define file locations that are assumed to be safe. Content, code, and add-ins are allowed to load from trusted locations with a minimal amount of security, without prompting the users for permission. If a dangerous file is opened from a trusted location, it will not be subject to standard security measures and could harm users' computers or data. If you enable this policy setting, all trusted locations (those specified in the Trust Center) in the 2013 versions of the specified applications are ignored, including any trusted locations established by Office during setup, deployed to users using Group Policy, or added by users themselves.  Users will be prompted again when opening files from trusted locations.If you disable or do not configure this policy setting, all trusted locations (those specified in the Trust Center) in the 2013 versions of the specified applications are assumed to be safe.