Yup, that's a great point. This article is based on a chapter from my book but this is chapter 6 out of 13 already. In earlier chapters, I discuss how we need to know the content, the goals of the text and what are the user's goals (read, skim, search etc.). Of course, we can't be 100% sure on their goals but we can take an educated guess based on the content we're designing with. Decisions like these should be based on that (+ personal preference of course).