I do this: #1 If anything in a pull request isn't blindingly obvious, ask a "why are we doing this here?" style question. #2 Encourage all developers to do th

I do this: #1 If anything in a pull request isn't blindingly obvious, ask a "why are we doing this here?" style question. #2 Encourage all developers to do this on all pull requests. #3 Get developers to answer those questions in the form of a pushed code comment rather than (or as well as) answering the comment. Make that an iron rule. IMHO this gives the best comments. I'd usually discourage comments that don't come about like this.