Managing Sierra to High Sierra upgrade

[Al_from_Ottawa]

Thanks for the warning about Time Machine drives.

1. Why Shared Users not Shared Users and Applications? My main reason for using a sandbox is to verify compatibility of applications. So what's wrong with leaving the applications I want to test on the internal drive? Should make it quicker to clone, with no obvious downside. Or will strange things happen if I update low level applications such as 1Password while running the sandbox? Their updaters could detect OS version and do different things, so that if I reboot into Sierra on the internal drive things won't work?

2. You say the High Sierra installer will update an internal SSD to APFS. What will it do with an SSD sandbox external boot drive? Not that it is really critical, because if I do switch permanently to High Sierra, I will be running the installer again on my internal drive and at that point I will get switched to APFS.