They are very useful in log structured merge tree (LSM) based storage. HBase uses them, for example. The idea is to have a bloom filter as part of each on-disk

They are very useful in log structured merge tree (LSM) based storage. HBase uses them, for example. The idea is to have a bloom filter as part of each on-disk component, so that one can look at the bloom filter first- and then only bother with searching the actual component, if there is a match in the filter. That way you can reduce the pain of having to potentially search multiple indices on disk.