There are at least two previous posts regarding the same 'issue' (if in fact it is one!), but I'm not sure anyone has got to the bottom of it yet. The agent suggested reinstalling macOS Sierra, which I did, but it didn't solve the problem. Unfortunately Apple Support was not very helpful when I contacted them this afternoon. And I have no idea why it reports storage content accurately on my wife's Mac but not mine. I would like to be a huge fan of Optimized Storage, but this set-up of counting iTunes media as 'system files' seems problematic. And I still don't have a separate iTunes entry. When I move things back into iTunes, they count again toward the System storage amount.

(The Documents content jumped up dramatically because I copied my iTunes Library to the Desktop.) Unfortunately, I haven't found a way to establish the separate entry for iTunes in this window. Now the System files are down around 8 GB. After I did that, my Storage report looked like this: As an experiment, I copied then deleted my entire iTunes Library from within iTunes. I could reach the iTunes folder through Documents on the left side, but the contents of the folder were grayed out. I also noticed that, unlike on my wife's MacBook Pro, I had no individual listing for iTunes. In a nutshell: When I go to 'About This Mac > Storage' the System files were taking up a whopping 90+ GB of my hard drive. I've encountered a problem on my brand new MacBook, but haven't been able to find a solution after working on it for most of today.

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