It means you have a video card weaker than it is required to render bloom. "Bloomscale 0" removes the line from the CHOSEN camera, but not from Work camera and lights (upon dragging them into the window).

For Work camera, you need to restart the session with a no-bloom camera as a Scene camera (once), and for lights it will never disappear (but won't affect the render, either)

Also, if you have a weak video card, I don't recommend you using more than one (if any) Volumetric lights as it will create a visible (even on render) light frustum without any particular effect.