Final Fantasy X-7 is broken up into several different chapters. Each chapter is then broken up into several missions that you can find by travelling to all parts of Spira. Within each chapter lies what are called Hotspots. These locations are necessary for you to visit in order to progress the story and carry onto the next chapter. Having said that, it should be obvious that those locations that are not Hotspots aren't necessary at all, but it is recommended that you visit every location in Spira during every chapter. Why? You'll find that there are several sidequests in each chapter that will give you different rewards, such as items, Garment Grids and Dresspheres. Completing all of the sidequests is necessary in order to boost your Completion Rating for the game.