There are certainly a lot of ways they can be used or not used, and people manage to use every single one of them. In my estimation they're good to use whenever they clear up potential ambiguity, such as in your case. A starker example comes from a movie title, "Eight Legged Freaks". Are they freaks with eight legs or are they eight freaks, all of whom have legs? The title doesn't actually make that clear, even though through context and general agreement we know that it means freaks with eight legs. However, you can completely clear any trouble up with a simple dash. "Eight-Legged Freaks". Voila! So whether or not people agree on how to use them, that is how and when I believe they should be used. Note however that this is a difficult one to remember when writing something, and is often the sort of thing a person only catches when proofreading.