It is perfectly fine to serve a roast chicken with no sauce at all, but a light gravy or jus will enhance its flavor. A jus is simply a gravy that hasn’t been thickened. In its purest form, it is just the drippings from the chicken. In authentic roasting— cooking on a spit—a pan is placed under the chicken to catch the juices, and that’s it. When roasting in the oven, the pan that catches the juices is the roasting pan itself, and because this pan is hot, the juices often dry and caramelize on the pan bottom. If the pan isn’t completely covered with the chicken and pieces of chicken, the juices can even burn. The chicken also releases fat that has to be separated from the juices.