>>105688483
It's about enforcing memorization and recognizing how to tackle the harder problems. You don't get that from 2h of khan academy. You do get that by practicing a lot and being able to solve such problems on an exam. That way in 2-4 years from now you can quickly re-learn and pick up what you learned before.

Personally the most valueable skills I've obtained from uni were in statistics and math because there would've been no way I would have bothered learning that outside of uni.