I was most excited about this feature, but the more I tried/thought about it the less I found any use for it.  Anything I wanted to change required recalculating (not reusing). I had a thread a while ago about this point and the only useful circumstances that was mentioned had something to do with animation which I dont do, so maybe you are right-do a search for the thread.
At the very least e-on should have implemented automatic checks - if you change something like lights it should display a warning if you try to reuse, and suggest reuse if you havnt changed anything in the list of 'no no's.

"I paint that which comes from the imagination or from dreams, or from an unconscious drive. I photograph the things that I do not wish to paint, the things which already have an existence."
Man Ray, modernist painter
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