We know that when we do backup for cassandra, we can do full bakcup with snapshot, when we need to backup incremental data , incremental_backup can do some help .
For snapshot we can just make snapshot for some keyspace/table. but incremental backup will do all data backup(make hard link for all sstable that flush from memtable or streaming ). we also know that commitlog's replay can do some keyspace /table 's filter.
So I think for incremental backup we also need some filter for it.After all not all keyspace/table is so important to do backup.