Not a GX owner, but I have an FJC and I'm very familiar with the workings of ATrac (and have coached many late model Toyota owners). I'll chime in on why you would want to disable ATrac argument.
I was leading a trail ride with a 4th Gen 4Runner with automatic ATrac on board. They came around a downhill left hander and the driver side of the embankment caught them off guard. The driver front tire climbed the bank, the passenger front dipped into the rutted trail and now they were teetering on front driver/rear passenger wheels. The driver rear tire was 4-5 feet off the ground. A quick reflex would have been to go hard passenger and GAS it, but they were not accustomed to this maneuver and panic stopped. At this point the vehicle is not moving and somewhat precariously perched.
My instructions to the driver were to hold tight the wheel at driver (where it was currently) and reverse slowly. The plan was to just level out enough to drive out of it. The problem was that ATrac wouldn't let it reverse at all - it was simply letting the vehicle continue to roll forward. In the end, I had the driver carefully turn the wheels passenger and GAS it down the hill. It worked, but it was dismaying to see that ATrac couldn't be over-ridden. Lockers would have saved the day here too.
I like having a switched ATrac so that I can manage expectations of what my wheels are going to do. When I need it, I turn it on, just like lockers.