Let's say you have too many folders in the iPhone and you have forgot what's inside all of them, or accidentally someone (i.e. your kid) move the applications around the home screen, or you want to cleanup your iPhone or simply you want a fresh start. One way to do this is to restore all the Apple native applications to the original layout and move out all the apps from their folders and put them all in the home screen sorted alphabetically, filling as many screens as necessary.
Just go to: Settings -> General -> Reset -> Reset Home Screen Layout.
Be careful in this menu, there are many resets and you don't want to reset something else you don't want. Also, the folders will be deleted but not the applications inside.