When you put the VR headset on and are in the car, often the view you have will not be straight. e.g. you look straight ahead but your view in VR is off to the left or right. Ctrl+space bar will centre the VR to the position of your VR view is 1:1 with your eyes.
So you will definitely want VR centering (Ctrl+space bar) mapped to a button on your wheel or button box.
There are not really any other VR adjustments or configurations that you would do in game.
But it can be helpful to map in-game functions or some keyboard functions to your wheel and button box which you can use while you have the VR headset on. Using your keyboard is almost impossible (unless you are a good touch typist) when you have the VR headset on.
In AC I have Exit mapped to a button on the wheel, so I can quickly pause when driving.
In DiRT Rally I do not use the mouse to navigate in-game. Instead, I have all the controls for navigating the game mapped to my wheel. This includes Enter, Esc, F1, F2, F3, F4, and the arrow buttons on the keyboard to move around the UI and menus. This enables me to control everything with the VR headset on.
In DiRT Rally I also have mapped to my button box the in-game controls for moving the seat so I can do this easily while sitting in the car with the VR headset on.