I am not inclined to spend hours (or even days) writing a definitive dissertation on data storage, storage media, and formats. Neither do I think you would want to spend the time it would take to read it. For the sake of brevity, suffice it to say:
- HFS+ format is optimized for Hard Drives (a.k.a. HDs or Rotating Rust).
- APFS format is optimized for Solid State Drives (a.k.a. SSDs, Nvme, and half a dozen other names)
- An HD may be formatted either HFS+ or APFS but data access will be faster if it is formatted HFS+ and periodically optimized.
- An SSD may be formatted either HFS+ or APFS and there will be little or no noticeable speed penalty in either format
- MacOS 11 (Big Sur) is completely dependent for its operation on structures and functions that are unique to APFS and the boot drive must be formatted APFS.
- When you are running macOS 11, external (non-boot) drives may be formatted either HFS+ or APFS
- A PARTITION is a physical allocation of contiguous space on a drive
- A CONTAINER is an allocation of space on a drive but it is not necessarily contigous space, and has at least one volume
- A VOLUME is a named directory that may contain multiple folders and files and can be assigned specific characteristics such as Encrypted, access privileges, etc. that are inherited by all the files and folders in the volume
- A VOLUME GROUP is a volume containing two or more volumes
