Some tracks are more hard on them than others, but I haven't heard much about any negative affects in NASCAR besides feeling dizzy or off balance for several hours after a race. Open wheel drivers commonly pull over 5 G's though in corners. Their heads are supported, but I would think your brain getting pulled to one side with that much force for over an hour can't be a net positive.

Not speaking negatively about it of course - to each their own. I raced Superbikes for eight years and you might as well throw risk tolerance completely out the window with that kind of racing.