Actually, I have seen a write time tree checker error on one of my file systems. I even reported the bug :) So it also has the benefit of ratting out btrfs itself when it's the cause. The file system did go read only, corruption didn't make it to disk, and it was fine following a reboot (it was the root file system so I couldn't unmount then mount; and this kinds of confusion can't be cleared with a remount).

https://patchwork.kernel.org/project/linux-btrfs/patch/024e4...