This is about the advised "Hard Reset" performed by touching the battery negative cable with the disconnected positive battery cable. I did a check of how much power is stored within the car's systems after I disconnected the positive battery cable: measured the voltage between the disconnected end of the positive cable and the negative cable (ground) and there was practically nothing, just some minor 0.01 volts which could have been false reading by the sensitive digital multimeter (Fluke); then I set the multimeter to "Milliampere" and tried to discharge whatever was presumably left in the car's systems by connecting the multimeter between the disconnected positive cable and the negative cable (also tried with the key in ignition-on position) - there was zero current flow. So, the touching of the cables may not actually do anything. The Service Training Course 682 shows the "Hard Reset" to mean just disconnecting the negative battery cable for at least 60 sec. and re-connecting:

 

As a mechanical engineer I'm a firm believer in anything electrical being fully functional until you let the smoke out.
The most reasonable explanation I've heard fro the extra step of touching the negative cable to the positive (connected) post is that it allows any capacitors in the system to bleed.
They'd probably bleed all by themselves but I'm not sure how long that would take. I'm also unsure about any ability to "see" any of these electrical blood letting events, even with a good meter.
Of course this could all be an old wives tale but electronics isn't the first phenomenon that's been the source of such tales...or, likely the last!

 

YES - a hard reset loses learned adaptations such as fuel trims and discharges capacitors. Touching the terminals simply accelerates this discharge process.

Graham

 

Last year, when my old battery was almost done for, the driver's door window wouldn't open and the sunroof would close automatically after I opened it.
When I did the hard reset, that was fixed...so there's at least one problem that can be directly solved by doing a hard reset.

 

Yes, it does have its use.
Fixing the messed up operation of the door / window controls is one for sure.
Loosing your radio pre-sets is an other .

 

+1 on the above. Also, on some cars it causes further resets e.g. of the EPB - which I think the X308 hasn't got.