They were emergency brakes long before they started being called parking brakes. It is common knowlege that in a case of regular brake failure the hand brakes ( emergency brake) could be used. You really need to realize the FSM doesn't tell you everything. Look it up online a see a hundred of explantions of the reason for emergency brakes by some very reliable sources like OSHA etc.not BS websites.. Yes using it as a parking brake is recommended.