Including fat in sausage can improve its flavor, texture, and shelf life, but it is not necessary. Fat adds moisture and richness to the meat. This makes it more tender and flavorful. It can also help protect the sausage during cooking and extend its shelf life. But, sausage you can also make sausage with lean meat and without fat. This can be a good option for those looking to reduce their fat intake or who are following a low-fat diet.