Only school Optimus with a MUX chip used to work just fine on my T420. For a long time the newer Optimus streaming through the (Intel) iGPU wasn't supported tra

Only school Optimus with a MUX chip used to work just fine on my T420. For a long time the newer Optimus streaming through the (Intel) iGPU wasn't supported transparently, but you could use indirect OpenGL using environment variables. I once used this for an application that required OpenGL extensions lacking in the open source Intel driver at the time. It's annoying and fragile. If you can let go of the battery runtime always running the dedicated (Nvidia) GPU is preferable.