The Fire does everything it needs to. Rooting allows Google framework and the Android market to work. You can also remove default apps you won't be using as well. That pretty much all it does.
You can sideload apps from other markets. We have a thread
here with links. I really see no reason for it. I do use Go! Launcher without rooting to have widgets and a Android looking home screen. It works well just wallpaper changes to default when you take it out of sleep.