Today in #FreeSoftwareAdvent it's ZFS. It gives me
• all in one volume management (no volume-groups and logical volumes and manually resizing partitions on those logical volumes with a dozen different commands, no playing the "oof, need more space on partition A and have too much free space on partition B, back up all the files, nuke both, shuffle partition-sizes/locations, restore the files" dance)
• transparent file compression
• transparent volume encryption
• fast and effectively free snapshots and clones (you start paying the cost if they diverge or deleting files that remain in a snapshot, but that's to be expected)
• same-disk redundancy with copies=2 to help prevent against bitrot, and multi-disk redundancy with effectively zero effort
• the CoW means no need for fsck(8) horribly slowing my boots or finding orphaned fragments of files and shunting them into a lost+found/ directory (my biggest frustration with OpenBSD's FFS2) in the event of an abrupt power loss
• efficient send/receive (beats rsync hands down in terms of speed)
• fine-grained quota/reservation control
• utilities make scripting easy with output-formatting options
• cross-OS support in a way that very few other filesystems provide (other than FAT 😆)
I'm sure there are additional reasons that didn't percolate to the top of my brain, but it's just so much more pleasant than any other disk management I've done on any OS.