Depending on the operator SOP and aircraft type, it may not be true to require both FDs off. Not talking Airbus here, OK?
e.g. an aircraft with a single FD input but dual displays - makes sense for the PF to take-off, say, in GA mode, while PNF stays on raw data. Both FDs on at safe altitude. On approach, PF uses the modes required, PNF monitors in raw data.
Reason being that a spurious FD command may be more readily noticed by the monitoring pilot detecting the flight path deviation.
Also 'looking through" the FD is too hard for this old-timer, though some seem to be able to do it. Unless following the FD commands, it goes OFF. Raw data is actually easier in some situations.