They're both for stopping. It's why they're biased to have more power in the front than the rear. You can take advantage of this with the rear to "tune" in so

They're both for stopping. It's why they're biased to have more power in the front than the rear. You can take advantage of this with the rear to "tune" in some situations, or to maintain stability at low speeds, but it should also be fully used when braking.