With centerAnchor={true} Flex starts behaving like a usual threejs element -
it centers itself on a position, rather than having this position as left-upper corner
Besides the fact that this easier to work with (now you don't have to do this manually via -width / 2),
the usecase is when you rotate the Flex to face the camera.
If you do it without the centerAnchor with position={[-width/2, height/2]}, rotation will behave like the center is shifted (when in fact, it's not)
With centerAnchor={true} Flex starts behaving like a usual threejs element - it centers itself on a position, rather than having this position as left-upper corner
Besides the fact that this easier to work with (now you don't have to do this manually via
-width / 2), the usecase is when you rotate the Flex to face the camera. If you do it without the centerAnchor withposition={[-width/2, height/2]}, rotation will behave like the center is shifted (when in fact, it's not)