My information is that reformatting HFS+ to APFS is only a matter of seconds or minutes because what is mostly replaced is metadata (not the real data). So goin

My information is that reformatting HFS+ to APFS is only a matter of seconds or minutes because what is mostly replaced is metadata (not the real data). So going from Sierra to High Sierra should be no problem with reformatting, but going back is a big problem then ;)