Some of this is a manufacturer being over careful, the early microprocessor equipment reacted very poorly to low voltage and voltage spikes such as you get during starting. Granted I am a dinosaur and have had programmable scanners in my vehicles since the Bearcat 101 in the early 70s but I also like to err on the side of caution. Both my vehicles have a SPST switch mounted in the dashboard. All the auxillary gear goes through that switch. After the engine starts the switch is thrown, before the engine is shut off, the switch is thrown. If I am sitting in the car waiting for something to happen I can just flip the switch and have my entertainment without every buzzer and warning light on the dash telling me that I am abusing the vehicle.
Simple easy and becomes habit.
I also went down to the local two-way shop and got a GE fuse block to run the supply wire through. If I have to jump start my own or another vehicle from my vehicle I pop the cap off the fuse block, pulling the fuse and avoiding having the remotest chance of spiking my radios, It will save many times the cost of the fuse and block.
Bruce