The purpose is to check your corpus for corruption, relevance and duplicates.
•it has got corrupted so what used to be good text is now just random characters or has got cut much shorter because of disk problems
•it isn't even in the same language as the rest of the corpus
•it contains too much boilerplate text
•it is or is not relevant to a particular area of enquiry
The tool works in any language. It checks corruption by using a known sample of good text (in whatever language) and comparing that good text with all your corpus.
See also : How to check corruption