Complex sentence: The Linux implementation of UnionFS is sometimes used as an ad-hoc snapshotting system and on LiveCDs as a way of overlaying a writeable file system on top of read-only media.
Split into simpler sentences: The Linux implementation of UnionFS is sometimes used as an ad-hoc snapshotting system. On LiveCDs it is used as a way of overlaying a writeable file system on top of read-only media.