Hopefully somehow maybe while they are in there they might do something to fix the nasty system lockups I have seen when starting both time machine and carbon copy cloner backups since switching to APFS. I'm assuming it is related to having >5 million files, but haven't figured that out for sure.
The symptoms are the system becomes almost totally unresponsive for up to 5 minutes to the point where you can't even drag and drop an existing window sometimes.