It is used commonly is spam detection and also known as nilsimsa code. A nilsimsa code is something like a hash, but unlike hashes, a small change in the message results in a small change in the nilsimsa code. Such a function is called a locality-sensitive hash. Therefore bulk hash data which is produced by for two similar text should be similar and comparable. Look at this example:

http://ixazon.dynip.com/~cmeclax/nilsimsa.html