"Switching off" is literally the opposite of what I'm looking for in playing RPGs, so it also makes sense that this mode simply does not compute for me.
It is perhaps important to note that it isn't just overall "switching off". It is going with the GMs flow on some things, yes. But that may mean you switch on to other things. Anything about play that isn't plot can get more focus time in a railroad scenario.
Kind of like on a road trip - if someone else is driving the car, you can pay attention to playing DJ.
If you are no longer worried so much about where the plot is going, for example, you can turn your attention to your tactical game, or characterization. Maybe you get to focus your thoughts on snappy wordplay, solving puzzles, or even the funny voice you want to use.