There isn’t as much choice in HFS+: you have just two devices for dividing a disk, volumes and folders. Volumes have fixed allocations of space which can’t be shared, whereas folders share the space of a volume. With a file system pulling no particular tricks with either, most users allocate the whole of each disk to a single volume.
With APFS, the choice is more complex:
- APFS Containers resemble HFS+ volumes, in that a disk is divided up into one or more non-overlapping containers of fixed size. Not only can space not be shared between two or more containers, but files copied to a volume in another container are true copies and occupy space in each container.
- APFS Volumes share space within a container, so that a 1 TB container can contain two or more volumes of no more than 1 TB each. Each volume has its own file system, though, and files copied to another volume within the same container are also true copies and occupy space in each volume.
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