Useful. One of the hardest things about learning a new language is getting the rhythm right - knowing where to put emphasis, where to pause for a beat, etc. This is why it's really really difficult to learn from a book; listening to native speakers is essential, or you'll find yourself running out of breath in odd places as you try to speak longer sentences (or at least, I do. My Mandarin gets way better when I've got a native speaker to listen to).