Snapper creates a Btrfs snapshot before any change in the root filesystem. If something breaks, you choose an older snapshot to boot from via grub.

By a bizzare coincidence, I just had a breaking update today. CUPS was missing some symbols and wouldn't start. Rolled back to an earlier snapshot and all is well.

I have to say, openSUSE introduced me to btrfs and while it isn't something i use often, when i do need the snapshot functionality it provides it is such a great feature.

The automatic snapshots saved me quite a lot to time on 2 occasions, where borked updates of the nVidia drivers resulted in problems booting the computer. On one hand, this should never happen. On the other, as long as nVidia does not improve, and nothing is going to force them, it is great to have such a safety net. It gets out of the way 99% of the time, but it is there when you need it, it’s great.

That's why Fedora also switched to this BTRFS snapshot model last year. It's slower than ext4, but much easier to rollback.

I got burned by debian btrfs upgrades, so I'll stay with ext4 though.

To add to the SP, the initramfs is kept on the same filesystem as everything else by default, not on a separate partition, so the initramfs is loaded from the snapshot too. However if GRUB breaks then you won't be able to boot.