While it's not strictly necessary to sear the beef before cooking it in the slow cooker for Italian beef, it can add an extra layer of flavor and help to develop a nice crust on the meat. Searing the beef on all sides in a skillet or on a grill before placing it in the slow cooker can help to caramelize the surface of the meat, creating a rich, savory flavor that complements the other ingredients in the recipe. However, I almost always skip this step and the beef has tons of flavor. When making the sandwich, the broiler also adds some crisp bits to some of the beef.