Linux systems usually consume more energy than identical systems with other operating systems
Is this true?
Yes, at least on battery powered PCs. Other kinds of machines may be more efficient on Linux but I guess these are mostly cases when there are no big and well developed proprietary solutions for them.
I don't have any information that proves it. I think in this list only hardware matters.
Surely use-case is important? Someone running a server that's on 24/7 vs. someone running it on a laptop or desktop that they shut down every day.
I was talking about comparing the efficiency between operating systems. That requires the use case to be the same. Comparing different use cases is unfair.