I think it would save you someday, when there is nothing writing in /usr so the writing in /home would not cause much damage. On a system with a huge root partition, an incomplete writing might damage the whole filesystem.
Fsck would be faster. newfs (mkfs) would be faster. I found NetBSD spend so much time when it do newfs a 32G root partition (installing NetBSD in hyper-v).
Also for the /tmp partition, we can use memory filesystem (tmpfs) if we have 4G of RAM or more, instead of physical disk to store things that are cleaned on reboot.
It doesn't make any sense.
Why staying on old package for unnecessary stability (that stability is for highly "mission critical" things).