Concurrent mode lets React render asynchroneously. It will batch updates and schedule render passes. If you give it an impossible amount of load, so many render requests that it must choke, it will start to manage these requests to establish a stable 60/fps by updating components virtually and letting them retain their visual state, using back buffers, etc.
It contrasts how web frameworks and even native frameworks work. Native has prioritizing and occlusion, but i know nothing that schedules as deeply as this.
The demo in particular schedules a react renderer for threejs (https://github.com/drcmda/react-three-fiber). But it applies to any other target as well.
