How to Address APFS in other key scenarios
1 Convert in place
Want to convert an SSD/flash drive to ensure it benefits from APFS? You can do it without erasing it (if its map is GUID), but back up its contents first. Select the volume in Disk Utility and choose Edit > Convert to APFS.
2 AirPort disks
A USB drive connected to an AirPort Extreme or Time Capsule won’t show up in AirPort Utility, and can’t be shared over your network; do not use Disk Utility on your Mac to convert it to APFS – keep it as Mac OS Extended.
3 Time Machine
There are no settings to change to have Time Machine back up a drive that’s APFS-formatted. Backups of your startup disk and other volumes should continue to take place as before, even if they are converted to use APFS.