>>295039210
The better question is why should you use SteamVR? The only redeeming quality it has is third-party plugins, which may not matter to you. 
Tere is some good free stuff though they're understandably tech demos. I recommend Wolves in the Walls, Mission: ISS, Crow: The Legend, Aircar (don't try this if you get motion sick), Spider-Man: Far From Home, and Dear Angelica. 

>>295039693
Yeah if you're running it on an Oculus headset you basically have to run two runtimes at the same time. Valve apparently has source code access to Oculus' runtime so they could easily do what OpenComposite does but better, letting SteamVR apps talk directly to the Oculus runtime, but no. It doesn't help that SteamVR itself takes basically equivalent the CPU usage as the Oculus runtime despite Oculus needing to run additional tracking calculations that Valve offloads to a chip on the headset and controllers.