For Linux power users, it's highly desirable to be able to completely customize your system. Sometimes, that can be best achieved from the start -- by piecing together the components that you'd like to include on your system. This way, as there are usually multiple programs that achieve the same result in different manners, you can pick those applications which you're most fond of. Most common desktop distributions don't make this high level of customization very possible (as it's not ideal and more difficult), but Arch Linux isn't like most distributions.