Your back consists of three main muscles, latissimus dorsi (middle back ), rhomboids and erector spinae (lower back). These muscles with other smaller supporting back muscles are a key figure when you are moving your body around. So It is a good idea to keep your back muscles in good shape. Lats or latisimus dorsi are located at the sides of your back. Lats help to extend, pull and rotate your arms towards your body. When you are pulling something, yourself up or just rowing the lats play a big role when creating the needed power.
When exercising lats, as in any exercise remember to do clean movements otherwise executing the exercise will start using other back muscles and muscles in your arms to deliver the needed power. And remember not to swing or rock your body in the pulling motions.