There's a bunch of compatibly reasons why this helps maintain portability across Unixes. But my favorite reasons for this are how much nicer it makes managing &

There's a bunch of compatibly reasons why this helps maintain portability across Unixes. But my favorite reasons for this are how much nicer it makes managing & switching between Linux images: > The merged directory /usr, containing almost the entire vendor-supplied operating system resources, offers us a number of new features regarding OS snapshotting and options for enterprise environments for network sharing or running multiple guests on one host. https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge/ https://www.freedesktop.org/wiki/Software/systemd/TheCaseFor... And indeed, with systemd one can boot a whole system from practically any unpopulated root mount with a /usr image mounted on it. Want to OS upgrade? Swap /usr & try it. /etc and /home and the other directories might have instance specific content, but the OS image is nicely set away & swappable in /usr. And one should be able to keep the same "instance" while swapping the image. It containerizes the OS image, separate-ish from the OS instancd, whereas before the OS was somewhat amorphously sprawled across multiple top level directories. It's a huge boon to manageability.