Well, just as I was about to order a new 27" iMac (replacing my geriatric 2009 Mac Pro), I saw some stuff on the Apple Developers Forum that gave me pause about my configuration. I was going for a top flight configuration except I thought a 512 GB SSD would be big enough. My current MP has the same size SSD with only half used. I tend to archive documents and downloads to another disk, although admittedly haven't cleaned up in a long time. I could save another 100 GB if I were better about that. Anyway, I recently saw some posts on the Developers Forum by people running the beta of HighSierra and there appears to be some problems with the APFS snapshots taking huge amounts of disk space. Now I know this is beta software and it could all be fixed before release, but it is making me re-think my choice of SSD size. What if even after getting the most serious bugs out of APFS it takes significantly more space. I could delay the purchase decision but I WANT MY NEW COMPUTER! Any thoughts?