I use it more as a general guide than anything else, but you quickly learn when and where it's useful, and when it's not. Quite a few times, it will err on the side of caution, having you brake too soon (a few times I've toyed with it, braking when it told me to, and came to a complete halt a hundred feet shy of the turn). And other times it won't "see" the next corner until you're right on top of it, thus the blinking comes far too late.
In either case, you eventually learn when to brake.. you learn what each car's braking distance is like, and you learn where you have to start braking early, or when you can afford to brake late. At which point it becomes little more than a reminder that there's a turn coming up. Which can sometimes help in endurance races when my mind starts to wander.. that blinking light will sometimes jerk me back to reality for a bit. Sometimes.. I've gone whole laps without realizing it before.. hehe.