That doesn't need to be engaged to charge the car as it only operates when you lock it, and charging is not connected to the car being locked. If the plug is still connected, the computer won't let the car go into READY state, though.
In some places, not those that use the J1772 protocol, an EVSE doesn't always come with cable and plug...the EVSE has a socket on it as well as the car, and you would then need to use your own cable. So, they implemented that function to lock the cable to the car. The original software never unlocked that plug from the car until the car was unlocked. This created some issues where people wanted to be able to share an EVSE. Say, you go into work, your car is fully charged in maybe an hour or two, and someone else wants to use the EVSE...they couldn't disconnect the plug even though the car was fully charged. So, they modified the software to unlock it when the car was fully charged, OR, if you unlocked the car. Personally, I'd like to have that be a user option, as if you're using your OUC or some other unit, it would remain locked in place until you decided it was good to release it. Now, if you were using your portable unit, once your car was charged, anyone could just unplug it from the car and walk away with it.