You can revert to the snapshot so there isn't really a problem, although that can be quite finicky and probably take longer to setup than the time saved avoidin

You can revert to the snapshot so there isn't really a problem, although that can be quite finicky and probably take longer to setup than the time saved avoiding fsyncs. Note that btrfs will be just fine on unexpected power outage - the filesystem will just contain some random combination of old and new files affected by the installation.