It is a fully compliant 40-amp 20FT J1772 plug with heavy-duty outdoor cable (3 power conductors, 2 pilot conductors). Use extension cable:
If the cable from the charging station you want to use can not reach your car.
If you have bought another EV and want to use the EVSE you have for both of them without having to move the cars around or reposition the charging station.
If your parking situation changed and it would be nice to have an extension for the EVSE you have mounted already.