There are places in the CMS where error conditions are raised and those errors are silently ignored. This can result in either an API appearing to behave correctly (as was the case with JMail before 3.5.1), the API making it easier for fatal errors to occur, or making debugging error states difficult because the error condition is masked. Examples of this include the getMenu(), getPathway(), and getRouter() methods of JApplicationCms in which if an Exception is thrown when trying to retrieve these objects the error is discarded and a null value is returned instead. A downstream consumer not checking $menu === null could try to use the expected JMenu object and trigger a fatal error trying to call a method on a non-object, whereas if an exception is thrown (either from the getters or just not catch any exceptions thrown by the underlying called methods), a developer can catch an error state and act on it with debug data and if this exception goes unhandled instead of a WSOD or PHP Fatal Error you'd at least end up on Joomla's error page.