Shrinking the filesystem is something I have never needed to do since becoming interested in computers in 1992. The only times I have really read about it is when people want to make room for a second OS.
I've seen people shrink filesystems to clone whiteboxes, and I can see some use cases in the embedded world, though these probably aren't the places you want to use zfs or btrfs.
To me, this doesn't seem like a big deal.