Yes, the subject is related to the G/V fan, as mr.bios questioned why the fan keeps on running (my answer in a nutshell: not the best technical shut down procedure). This is why the subject got much more wide, and this is normal and typical in any forum thread.
I think you give especially scooter batteries too much "confidence". They are very small in capacity, and if they are a bit of age you can damage/drain them very quickly. I have learned over the more than 4 decades of riding, that one should ALWAYS fully respect the limited capacity of any battery, and not take the "best situation" for granted, rather the worst. Also, no matter if you think it is fully charged after a ride, it may have perfect Voltage, but Voltage is not the issue, it is Amp-hrs capacity remaining to operate the system, starter, fan, lights, or sometimes all at the same time.
Let's say for any reason the bike does not like to start "as usual" (bad fuel, it fell over, etc...) and it is hot outside, wouldn't you not want to have ALL the possible battery capacity to get it back running again, especially when with a Grand Vista you can't push-start? So, here we come to my opposition of using the kill switch: if in hot weather the fan keeps on running, one talks to a neighbor, and the lights are still on, and at the same time one holds the brake lever (which activates the more power consuming brake light); doing this for a minute a weaker/older battery has probably used up already quite some capacity for really "nothing". If one goes click, click (kill - ignition switch), I have no problem, but why not use ONE switch (except your argument for programming the brain for an emergency situation; but for how long do you need to program? years?)....
I have seen with my own eyes exactly the above example mentioned and then the rider wondered why his Cruiser did not start and the battery had not enough capacity. I agree with you, a newer healthy battery wouldn't have much issue with it, but use of "capacity" is also ONE factor in "life expectancy" of the battery. The less stress on the battery during its life, the longer it lasts. FYI: I just yesterday replaced a battery that had perfect Voltage but NO capacity any longer. (cranking amps)... it was 11 years old when it "quit". With that said, I think I have done something right