Currently, quiz answers can only be released to the entire class at a time (or whatever subset of students who have been assigned the exam).  When students have problems in the middle of a quiz, instructors often need to give them another attempt to finish the quiz.  Depending on how long that process takes (sometimes it could be weeks depending on the student and the issue involved), that means that the rest of the class is stuck waiting for the instructor to release the answers to the quiz.

This idea is to allow instructors to selectively release quiz answers to some students but not others (like those who have been offered an additional attempt).