Here is a snapshot from the online Model X Owners Manual.
Even with the "Energy Saving" feature turned OFF, which seems to prolong the period of time that the internal 12V accessory power outlets remain energized when the car is in park and the driver and key fob are away from the vehicle and the various doors are shut allowing the vehicle to "turn off", the vehicle will still shift to an energy-saving made overnight.
It's been my experience that during this time, even with Energy Saving set to OFF, the internal power outlets are no longer energized. I own an early production AP1 P90D Model X delivered in March 2016.
Of course, I prefer to have the vehicle set to "Always Connected", but I wanted to be sure folks were aware of this. It's possible the behavior has changed in the last year of software updates, as I have not tested this on my vehicle since 2017.