This is a very real threat albeit generally rare, of course. As long as an electrical circuit has power it can begin to heat up wires or connectors due to bad

This is a very real threat albeit generally rare, of course. As long as an electrical circuit has power it can begin to heat up wires or connectors due to bad contacts or worn threads, for example, even if the car is cold and has been sitting for days. In the lucky case there's a slow short that just drains the battery or burns out the wiring, stopping the generation of more heat. In the worst case the heat will melt something and provide a new, direct short to ground, which runs enough power through the wires to ignite something. I have a garage for doing repairs and maintenance on my cars. Each time I park one of my vehicles (new or old) there I'll disconnect the battery negative cable and keep it disconnected unless I have to start the engine or connect to diagnostics. I have insurance, of course, but the idea of my shop burning down alone is enough of a deterrent that motivates me to do the small effort of disconnecting the battery. I really don't want to rebuild my shop and reacquire all my equipment because of a bad connector hidden inside the wiring harness somewhere in my car chose to fail.