The function tries to stop the server-wide journal writing. Once the journal writing has been stopped no transactional control can occur. So this function has to be used with upmost care. Typically you may need to call this function when uploading your exiting tables to Caché via APPEND FROM... command and you are sure that no significant activity is being performed elsewhere. The call to this function prior to APPEND FROM.. reduces the upload time considerably. Once the job is over, you will have to call CachéStartJournal() to reverse the process.
Please note that there is no way to inform the database to start journalling automatically once it has been stopped. So your code is responsible to handle this request itself.