We do that on pot roast for the best flavor.
Edwin is correct as a little research on my part has shown. I did find a reason to sear however.
"Browning is very important when cooking meat, but not for the reason that you might think. For at least a hundred years, cooks have been taught that searing, or browning, seals in juices. But it doesn't. Harold McGee, the author of On Food and Cooking (Simon & Schuster, 1984), demonstrated conclusively that meat loses about the same amount of juice during cooking whether it is seared or not.
So why brown meat? Because it creates a tremendous amount of flavor. This happens through a process called the Maillard reaction, named after the French chemist who first described it in the early 1900s. The Maillard reaction occurs when the amino acids (protein components) and sugars in meat (or almost any food) are subjected to heat, which causes them to combine. In the process, hundreds of different flavor compounds are created. These compounds in turn break down to form yet more new flavor compounds, and so on and so on and so on. It's kind of like rabbits multiplying.
As it turns out, each type of food has a very distinctive set of flavor compounds that are formed during the Maillard reaction. In fact, it is these same compounds that flavor scientists have used over the years to create artificial flavors."
