If you understand a derivation or go through it, you'll understand the assumptions and hence the scenarios where it will be valid. A good engineer is someone who is able to effectively model a situation/scenario and derive equations that govern the systems dynamics or behavioural characteristics. If you can't do this and just remember x number of equations at the end of your degree, what skills have you actually picked up?
Also, those who know the derivations tend to do better in exams as they better understand when and where each equation can be used and are able to justify their decision.