Mystery of the FIRST_ROWS hint

I've always been intrigued by the FIRST_ROWS hint, so I paid special attention when we reached it in the 11g SQL Tuning class. But I'm still puzzled.The course notes said that although you shouldn't be using hints generally, when you do, FIRST_ROWS is the most useful of the hints (in the form FIRST_ROWS(n) where you specify how many rows to optimize for). Also that it's not effective when the