It is a trick used in certain data-mining applications. You denormalize your "live" data into a number of additional tables and you do your data-mining queries on these denormalized tables. It is very fast as there are much less JOINs to be done when querying the data, but you are limited in what you can query. If you do this denormalization as a batch job when the database server is not very busy (say every night or week-end) and put the additional tables on another server optimized for read-access, I can see the benefit.

The drawback is that the data becomes stale as soon as the live server updates and that not all queries are possible because you see the data through the mirror of the denormalization process. Sometimes this is even considered a benefit: "Now you can get at your data without having to write SQL." Yeah sure what a benefit ...