Well, truth be told, this is not so much about walking in rhythm (which was a wonderful song by Howard University's Donald Byrd and the Blackbyrds a while back--check it out at http://www.youtube.com/watch?v=Vxg-a8a2UuY) as it is about paying attention to rhythm in writing.
Now, I'm not talking about the rhythm of a sentence or the rhythm of speech reproduced in prose or even about rhythm in poetry. Those are important because without rhythm in our speech we would sound like one of those robots or androids in a sci-fi movie. In a related matter (I'm digressing--shocker!), don't you just hate it when you make a call to some business and you get one of those voice recognition programs that can't recognize its own mother? I want to say, "No, I won't say 'one' to speak to a person. Let me press 'one' please for the love of mercy." To which the robo-speaker replies, "I could not understand your comment. Please repeat. To speak to a person, say 'One...'"
Or worse, when you're trying to get the thing to understand where you want to fly.
Robovoice: "Please speak the name of your destination."
You: "I want to go to Washington, D.C."
Robovoice: "You want to go to Washington State. Is that correct?"
You: "No, I want to go to Washington, the District of Columbia."
Robovoice: "You want to go to Colombia. Is that correct?"
You: "No, I want to go to the CITY of Washington, D.C."
Robovoice: "You want to go to Cincinnatti, Ohio. Is that correct?"
You: "No, I want to go to Dulles Airport near Washington, D.C.!"
Robovoice: "You want to go to Duluth, Minnesota. Is that correct?"
You: "No! Is there a person I can talk to, please?"
Robovoice: "You want to go to Paris, France. Is that correct?"
I think you get the idea.
Anyhow, this post is about the larger rhythms of prose writing, specifically, the rhythm of using description in which you as a writer (hang on here) describe things for a while and let the pace of the story marinate in its own goodness for a while, and in using exposition in which things happen and the story moves ahead. I suppose it would be possible to use all description in a story but not much would happen. We would have some nice description a flora and fauna or people in a city, have no idea as to what was going on. We as humans want to know what's going on.
Conversely, if we had only exposition, we would know something was happening but we wouldn't know where or when or why or wherefore it was.
Here's the point: we need both in some sort of larger rhythm to keep people reading and to help them understand in an immediate and, in a larger sense, in the immortal words of Marvin Gaye, "What's Going On." (http://www.youtube.com/watch?v=jzPA-FrVu3I) When to use each is a matter of judgment. So break out some rhythm in your story. You will happier and your readers will, too.