Quote - ... make no sense...

Well, actually the original concept now makes sense to me. It was an easy way of making reflection maps (which would otherwise be uniformly self-lit) dependent on scene lighting in a somewhat reasonable way. I agree it makes no sense to do things this way nowadays.

Of course it won't work in bb's example scene; there is no diffuse light in the scene, so the reflection map is always multiplied by zero. But in reality an object that is visible (glowing) with no external lighting must itself be a light source, and with that light source correctly modeled in the scene the 'reflecting' ball would not be black.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)