I'm not talking about getting more in-depth explanations or clarifications about class material, I'm talking about: "If I were you, I would really focus on that exercise on page 47 (wink wink). Also, just skip chapter 4 (wink wink)". This creates a scenario where a student with genuine subject mastery can actually be outscored by someone who simply got the hints.

To answer your question, I don't recall ever going to "office hours", as I was generally a top student with minimal effort and an autodidact, but I learned about it through friends. Having parents who are both professors also gave me a front-row seat to how common this was.