Definetely certain subjects are far better 'understood' than learnt for the exams.
However, Air Law is a cracking example of next to useless information on the whole. It is unlikely in the real world that you need to know which convention deals with damaged caused to persons or property on the ground by foreign aircraft. However, knowing who has right of way when overtaking or which is the standard direction you both turn if you meet oncoming traffic is useful. To that end, I am going back over Air Law at the moment while sitting on my hands waiting for initial Type Rating.
Systems is an important subject which would be useful for airline interviews & type rating I imagine. Although again, you can be much more selective on practical knowledge when going back through them after your exams.
PH.