Kinda makes sense. I really don't like all this automatic bull****, but it does make saense.

Like a pedal, if there is no inpput, turn off and save the battery.

with an amp, if nothing is plugged into the output, wwhy have output ?

I reember a car amp a long time ago, simple, transforer based, push pull with a driver transformer. It put out some, and they said to run the main power to oit off an always hot line in the car so you wouldn't overload the ignition switch. The other wire could come from hot in acc or run, ar even the new thing coming out on aftermarket radios, the pink wire that became hot when you tuen on the radio. It also ran some power antennas. The "ON" line for this amp simply supplied the bias circuit. With the bias off, it is pretty much off and that asa that. No relay, no pulling 20 amps though youi ignition switch, none of that. (it went in the trunk (under the boot))