I've long thought that most "opinion" books -- self-help, historical analysis, scientific commentary, policy-recommendations etc. -- are 3-5% the actual point they want you to take away, and 95-97% of the material is the anecdotes/cites they use to try to convince you they're right.

Agreeing with the article, you don't need to remember the justification nearly as much as you do the bare facts. Except: in the future, remembering some of the anecdotes helps you remember why you believe what you (now) believe in the first place. It also helps you convince other people of the rightness of the ideas.