It is totally optional, but not necessary. We usually do not sear the roast out of total laziness. However, if you do sear the roast it will absolutely add to the flavor! When you sear a roast, you caramelize the natural sugars on the outside of the meat, which will give an extra rich flavor to the finished dish. So if you have the time and don't mind washing an extra dish, go ahead and sear your roast on all sides in a large skillet over medium-high heat.