Let me take this discussion in a different direction, away from talk about which details to learn, to talk about the methods of learning. It is true that a pass/fail curriculum means you are not beholden to the homemade slides and questions that your professors write, so you do not have to stress about the nitty gritty that separates the middle of the bell curve between 88 (high pass) from 90 (honors). That's nice.
The most important difference, in my opinion, between studying for class versus studying for boards and life is that the latter requires long-term retention. You can memorize slides in an intense few days before exams and do extremely well on your course exams. If you do not review that material, however, you will promptly forget it. For select high-yield material, you will have to relearn it again for your classes the next year, for boards, for shelf exams.
The most efficient way to develop long-term retention is through purposeful, spaced repetition of retrieval practice (e.g. Anki). Such a method requires an additional investment of time. You will be doing a little review of anatomy every day even though your anatomy class ended a month ago. You have limited time, so you must prioritize the material you learn. Only purposefully use spaced repetition for high yield material.
The freedom that a pass/fail system allows is that instead of learning 90%+ of a mix of important and unimportant details and promptly forgetting a mixed bag of a third of it by a few months out, you can spend just a little more time to learn the most important 70-80% and make sure you hold on to all of that for the long term. With spaced repetition systems, you control what you retain.
The question is, what do you choose to learn, and what do you choose to retain? You will develop an intuition for what is important over time. First Aid is an excellent starting point. It is a guide to content; it is not a primary learning source. Yes, you can and should "memorize First Aid", but reading First Aid should not and cannot be the fundamental basis of your learning. First Aid gives you structure and points out key facts. Watch a lecture or read a textbook or browse an article on UpToDate, all while cross-referencing First Aid to ensure you understand the basis for all the important facts. For those important facts, do flashcards and questions to solidify that understanding and move those memories from short-term to long-term storage.
This is the learning method of the future, but only a minority of current med students will appreciate the flexibility of P/F curricula through such a lens.
