Right, I think the main issue that memorization solves is that it can look bad if you stumble or pause for too long while you're trying to explain something. While it's not necessary to memorize stuff you write down word-for-word, it's important to at least know all the key points that you need to bring up and smooth ways to convey those points.

Basically, "I need to answer X, and phrase Y is a good way of saying it", rather than "Better memorize this 5 sentence script answering that question".