Overidden virtual functions should have exception-specification at least as restrictive as its own. A caller function might not be able to catch if derived threw an exception that was not advertised in the base class function.
Thank you for your interest in this diagnostic message. We are still in the process of documenting this specific diagnostic.
Please let us know of your experience with this diagnostic message by posting a comment below. Your interest in this diagnostic will help us prioritize the order we document diagnostics.