Atomic operations are about more than just torn values, so while I agree with you and other posters that I am not aware of an environment where torn bool is a possibility, there is more at stake.
Herb Sutter gave a great talk about this which you can view online. Be warned, it is a long and involved talk. Herb Sutter, Atomic Weapons. The issue boils down to avoiding data races because it allows you to have the illusion of sequential consistency.
