I never liked writing exercises. I always thought they were a waste of time. But lately, I have been REBORN. A true believer in these little exercises. I think they are especially good for dialogue. Sometimes we try to do too much with dialogue. I've been guilty of puffing my story up using dialogue. You know, thinking lots of talking will fix my problem. We want convincing dialogue. Sometimes it's best to hush up. You can't center your story on conversations. It needs a lot more.
So back to the exercises. They are helping me to see when and how much dialogue I need. Have you ever tried writing a story using nothing but dialogue? And only add detail, scenes or otherwise, through your spoken words. It's hard, but fun. It will help you to see that using dialogue is only one facet of writing a book. And after you have written your scene or even an entire chapter using nothing but dialogue, then cut,cut, and cut some more. You'll be left with the bare bones and the most important dialogue you'll need. Words have meaning. Use all your words wisely. :)