Whether boosting or lowering resolution, the process is simple, according to Steam's blog post: SteamVR runtime measures your GPU's speed and instructs applications to render at a resolution appropriate to its power. For users with graphics chips that can't render their headset's native resolution, SteamVR will down-res it (but not lower than the Vive or Rift's native resolution).

It's good to see SteamVR moving past adding digital tchotchkes to improving features, like adding support for Windows Mixed Reality headsets and a YouTube 360 video app. The new autoresolution is live in beta, so you'll have to opt in (find SteamVR under Tools in the Steam Library and right-click to find 'beta' in properties).