For some people it perhaps don't make any sense to have a Cockpit setup and use VR at the same time !
But for me it does !
Spending many hours in the cockpit you know more or less where all the knobs and switches are placed. When you are having your VR glasses on I just reach out to the switch or knob and moves it. In the VR cockpit you can see the switch move as you move the real one. The most common ones are those on the MCP, EFIS Throttle and so on.
Today i'm using PMDG 737NGX and it's possible to interface nearly all your hardware with this add-on.
CPFlight MCP and EFIS are the easy ones, they just connect with their own driver.
MY CFY Throttle also supports PMDG directly
OpenCockpits devices are connected trough OC4BAv4
All the switches in eg the Overhead and so on has to be connected to Joystick interface card that windows and FSUIPC can see. Most common one is the BU0836X card.
Trough FSUIPC you can assign all the different switches and buttons. Each switch has it own ID and a code for on/off.
This document covers the most of the switches and buttons