Hardlinks can be used to create duel systems that have a total size that is much smaller than the sum total of the two individual systems.
I've used this principle already to create a sfs file that contains both a pristine Puli/Xenial64 and a separate Rootfs that has the core libs upgraded with those contained in @wiak 's W_LGO.
It occurred to me that rather than having a dual system where one system is an upgrade of the other, I could have dual systems with smaller differences. For instance the systems might only differ by the package manager or alternatively perhaps one system uses the multi-arch folders and the dual system uses the symlinks hack.
I could do this (and I might) with the Fosapup W_LGO or I might use something like woof-next to build the dual system. The advantage of using woof-next is that I can get a separate file listing for each package. Puppy doesn't do this because in puppy some of the packages are grouped together in a file list (e.g. glibc) and this is problematic if I wanted to use dpkg to upgrade glibc.
The logical groupings in puppy are helpful for building a distro because it simplifies what one needs to include vs exclude. However, it can present problems with some things that one might want to do with a package manager