I didn't know it could be turned off.
But I'm basically the same as everyone else here, I use it to learn tracks how my particular car of the moment works, and then go from there. I still always observe it (if other people drive from a view with it in view, I couldn't imagine missing it), but I often find by lap three or four, I am going faster than it suggests.
Also it can be off, to those serious racers, since in the nicest vehicle, it has to choose between 8 gears, so if you are exceeding the recommended speed for a turn by 1 mph in a four or five speed, it's going to drop and will be a bit off. Quite a few times I have down shifted in a vehicle to match, and I grind gears when I could have handled it. Also, I have been in low gears and the red suggests higher, ie taking a turn near red line in 3rd and it tells me 4th instead.