I came across many children who keep on studying the same concepts and who keep on practising the same questions as they wouldn’t get confidence. They do this at the cost of other subjects or questions. i.e. they don’t spend sufficient time on other concepts/subjects.
If they know the correct methodology and the number of times to study a particular concept, they save a lot of time. The time thus saved could be productively used to study other subjects, to participate in extra-curricular activities, to pursue hobbies or for personality development.