All the knowledge that is tested for is necessary. Some of it is however deadly dull to aquire. The lad passed at 100%, not easy. Every other subject can be made interesting by a good instructor, and many students will go deeper into the matter than required. I've been instructing a while now, and still have to force myself to keep up to date on air law. To judge from the frequent discussions on this forum, most people seem to find air law the hardest to assimilate.
Learning never stops, on the ground or in the air. The day it does is the day to hang up your headset for good. Enjy the flying!