Howard Oakley takes stock of APFS in High Sierra both good and not so good. If you have the slightest interest in APFS read his posts. The quick summary is that if your Mac boots from a SSD, you can reap the Clone and Snapshot feature benefits of APFS which can be substantial.

If your Mac boots from a Fusion Drive or hard disk, you are in limbo because Apple has not completed APFS Fusion Drive/HD support.  Oakley warns of potential, “adverse effects of copy-on-write, perhaps the single most important technology behind APFS” on hard disk media and concludes

you can see why the performance of APFS on rotating disks is far inferior to that of HFS+. That is, though, something of a worst case.

But there is more. APFS brings yet more changes to basic Finder behaviors.

Apple has made Finder’s simple human interface progressively more complex. Originally:

• Dragging an item from one folder to another on the same volume moved it; to copy you Option-dragged.
• Dragging an item from one volume to another copied it.

Children of all ages, myself included, have found those principles clean and simple, and quite fail-safe.

Now, rules have become:

• Dragging an item from one folder to another on the same volume moves it.
• To make a copy (not clone) on an HFS+ volume, Option-drag to another location.
• To make a clone (not copy) on an APFS volume, Option-drag to another location, but I can’t see how to make a true copy.
• Dragging an item from one volume to another copies it, unless either of the volumes is on iCloud Drive, in which case it moves it.
• To make a copy (not clone) to or from iCloud Drive, use Option-drag instead.

Messy.

I agree with Oakley’s final summary that we’ll have to wait and find out how serious Apple’s commitment to macOS really is. High Sierra is not turning out to be the next Snow Leopard. Not by a long shot. Will macOS remain a serious platform or become an iPhone accessory?