VR rendering does not work the same way, as you know it from game rendering on a 2D display.
In VR, the pixels of the rendered game frame do not get matched to the display panel pixels. First, several other things happen, distortion correction being one of them and you’ll end up with a very different mapping from game resolution pixels to pixels of the actual VR display panels.
The higher the resolution of the rendered frame from the game, the more precise the mapping to the final display panel will be and the clearer and better the final image in the VR headset will look.
As a side note, for regular 2D display gaming, although the mapping of rendered frame to display pixels is 1 to 1, that doesn’t mean rendering at higher resolutions than native is “wasted” there either. Although there are diminishing returns, the frame will look better if you render at higher resolutions, because it will allow the final pixel color values to be sampled from several points within a pixel, instead of the center of the pixel. Rendering at higher than native resolution will give you the visually best possible anti-aliasing, best possible texture filtering, etc. although at a high cost.
If you have GPU power to spare, rendering at higher resolution will always yield the visually best results.