You can boot straight into snapshot, may be useful if an update went wrong or you don’t like new kde.
You can change drives and raid configuration online. For example I bought a laptop that had windows preinstalled, so I used the second half of the disk space for linux, then I figured I don’t need windows so I formatted windows partition to btrfs, added it as a new device, moved all the data there, deleted the old linux partition and extended the new one to the whole drive, all that easy and without reboot.