Sometimes, even if you've slowed down, you'll find yourself in a corner that's longer than you expected, and you'll be sliding out towards the edge of the track. One that doesn't have a friendly Armco barrier and instead features a selection of ramp-like rocks. Often in this situation, you can simply 'get out of the throttle' and regain traction. In other words, let go of R2 and keep turning.
Again, it's about transferring the weight to the front wheels. It sounds like it wouldn't make much difference, but it really does, allowing you to rescue corners without hitting the brakes. And because you're not actually using the brakes, you'll carry more speed out of the corner, which is what it's all about, after all.