On something like a Cessna 172 / 182 it would make total sense to unlatch the door, because in my eyes the design is poor, if the internal door lever is pushed down flat to the armrest to lock the door, it also locks the external handle meaning outside assistance cannot physically open it.
If the door is cracked open and the internal lever is then put in the locked flush position, if memory serves me correctly that should prevent the door from physically shutting as the latching arm will be protruding.
If you fly them try it... it may come in handy one day.