The clustering function analyzes a result set and groups rows into clusters so that the rows in each cluster are semantically more similar to each other, on average, than they are to other rows in other clusters. Ordering rows by subtopics can help you get a sense of the major subject areas covered in the result set. Clustering is only available with the Enhanced Full-Text Search Specialty Data Store.
Returning a clustered result set can be significantly slower than returning a nonclustered result set. If the response time of a query is critical, use a nonclustered result set.