In a grill pan, you can grill pieces of meat and other ingredients at a high temperature. The high temperature lets you quickly sear your ingredients. That's useful, so you retain all the juices and you get a crispy result. The cooking surface of a grill pan often has ridges. This way, you get the familiar grill marks on your pieces of meat or fish. The ridges also catch the moisture and grease that's released, so you always grill grease-free and you can easily clean your pan after use.