Through Jailbreaking the operating system found in Apples mobiles i.e. iOS, can be modified for running unsigned code to access files which would normally not be possible because of Apples policies. With this Jailbreaking feature it would be possible for you to run application installers on your Apple device like Cydia, through which you can download third party applications, extensions that are not available in the app store from Apple and tweaks. It will provide you with unlimited possibilities to do so many things on your Apple device which would not be possible with a non-Jailbroken device.
Extensions can be installed which will provide instant access from your Apple iOS device to the system settings, bypass all the restrictions placed by the carriers and Apple, and get hold of packages where gain control and increase your iOS experience. It is all about getting away from the restrictions and install whatever you want, anytime.