The cheap snapshots and data integrity verification are nice.
Most distributions & systems don't allow ZFS out of the box and ZFS is *very* user-unfriendly in how much administration/configuration it needs.
btrfs fullfills the niche of "what if I want the properties of ext4 data=journal on RAID10 except not dogshit slow and with integrity verification & repair that actually works (and doesn't incorrectly depend on hardware to send errors on mismatches that much modern hardware doesn't anymore)?"
