By "hot-swap" I mean ensuring that the new battery is connected in parallel to the old battery while the old battery is removed and the new one is installed in its place. The idea is to ensure that the vehicle electricals/electronics are never without battery.
I've seen mechanics do this on a few Japanese vehicles (2008 Nissan Pathfinder, 2009 Mitsubishi Pajero).
I have also heard of one person lose central locking on his 2007 Nissan Patrol after failing to hot-swap his battery out during a replacement DIY.
Are these observations some kind of urban myth or are the vehicles designed like this from the factory? If yes, why? If not, why do mechanics (even at dealerships) observe this practice?