It depends on the subject and what you're studying. Many subjects are like learning the piano - if the only time you practice is when you're having your lesson with your teacher, you will never develop real competence or improve beyond a surface level. That said, everyone needs different levels of reinforcement, and the one that's picked by a teacher is often arbitrary both in focus and in timing, so if an individual student has a more optimal way of doing their own reinforcement, they should be encouraged in that.