By default the changes you make in Lightroom are saved within the catalog, and not alongside your images. This means that if something happened to your catalog (it became corrupt, for example) then you would also lose all of the changes you made to those images. By saving the EXIF or “side-car” files with your Raw images, you can prevent accidental loss of the data and edits you have made to your images, such as develop settings, virtual copies, and more.