The notion of "Study Guide" was unknown to me before moving to the US (I don't think I was ever given one during my studies in France).
I believe that the goal of a study guide is three-fold:
To list all the topic that will be on the exam,
To provide some hints to the students as to how to revise,
To help them deal with their stress.
In the case where everything that was covered so far will potentially be on the exam, I feel like students shouldn't need one: they should be able to list all the topics by going through their notes (or through my detailed syllabus), they need to learn how to revise on their own (it is difficult to have a "general recipe" that works for everyone), and they need to learn how to deal with their stress on their own (I'm talking about college students).
Of course, during class, I gave them plenty of advises, examples, problems, partial feedback, and highlighted what the key ideas and critical topics are. They had multiple short tests (quizzes) and projects, and I went over them in class. I tried to help them assess how well they know the content of the course during class, and I am open to meeting them. I know that teaching is about repetition, but listing this information once more doesn't seem so useful to me.
Am I overlooking one aspect that make study guide really critical to students? What is your personal practice?