I was taught to do this in open-wheel racing. Thumbs stick straight up rather than gripping inside the wheel. And on bigger crashes, completely let go of the wheel as quickly as possible.
My dad taught me that when I was learning to drive. What's the last thing you do before impact? Let go of the wheel.
And, counter-intuitively, get off the brakes! This returns/angles the nose of the car up, which can be the difference between life or death if colliding head-on into a larger object (like a deer).