What are the benefits of iPhone jailbreak?
What is jail breaking? Why do people do it? What is the advantage and disadvantage?
It is mostly done to escape the restrictive nature of the App Store. Once you have jailbroken an iPhone you are free to install a lot of software that apple would not normally allow. Such as modifying the lock screen to display useful information, or enabling multitasking on an iPhone 3G.
Jailbreaking is to break out of the "jail" that Apple runs normal software in so you can do unauthorised modifications such as install your own applications or alter system components. Jailbreaking is often done by exploiting security issues in iOS and such are closed with the next software update.
If you jailbreak your iOS device the device is unsupported. While it's not illegal Apple has explicitly stated it's entirely your problem for any issues you cause. (The Genius bars won't touch a jailbroken phone unless it's been restored and the problems exists on a non hacked version of iOS).