For other than consistency, if APFS-->HFS+ -->APFS produces a bootable clone and bootable restored volume (isn't that the … HFS+ -->APFS second part?), why change the HFS+ to APFS?
More specifically, if the computer HD is APFS and the backup/cloned drives are HFS+, why change the backups?
Because you'll lose the benefits of APFS.
For example:
- Time and date stamps will change (APFS allows more precise time/date stamps than HFS)
- The backup may balloon in size, becoming much larger than the APFS source (because HFS doesn't allow space sharing and file cloning)
- The backup may lose APFS snapshots (I'm not sure how a snapshot will be copied to an HFS volume, or even if it can be)
- APFS allows very, very, very large numbers of files on a disk and in a directory. HFS has weird problems when you get millions of files in a single folder, something that happens to my partner Shelly on a regular basis when she uses protein modeling software in her research. If you copy a drive with a very large number of files to an HFS disk, you may encounter problems.