It seems to make the head shake more. That's it.
I first thought that it might actually look into the direction you're driving (e.g. very useful in sharp corners), but all it does is make you head wobble more.
I'm afraid it's another attempt at simulating a CAMERA, instead of HUMAN VISION.
What people often overlook when trying to simulate what they see on YouTube (e.g. when it comes to FOVs or head movements), is that we have a BRAIN. And that brain is pretty impressive in what it does (at least for most people). Even though our head may shake or tilt, our vision processing will compensate for that, and what we actually "see" is a pretty stable and level image.
But those "camera simulations" seem to forget that, and what they are presenting to us on the screen is what a camera would see, but, since our brain now doesn't have the physical feedback anymore, to compensate for those movements, it will look confusing (and vomit-inducing for some).
The game actually gets it right with it's "unrealistic" stable view. That's how we would perceive it when viewing the situation first-hand — not all shaky like through a dumb camera.
Unfortunately, Codemasters made the same mistake (of replicating a camera view) with the rain effects. I've never driven through a rain storm that looked as disorienting as any few drops in the game look. But that's because in real life you basically look through those drops on your windshield (due to your 3D vision, and your focus being far ahead) , and will hardly notice those drops. But that's another topic...