What's the purpose of jailbreaking an iphone?

Is it true that it will make the apps and ibooks free once your iphone/ipad was jailbreak?

IOS jailbreaking is the process of removing the limitations on Apple devices. One of the reasons for jailbreaking is to expand the feature set limited by Apple and its App Store.[9][dubious - discuss] Apple checks apps for compliance with its iOS Developer Program License Agreement before accepting them for distribution in the App Store.[10] Jailbreaking permits the downloading of programs not approved by Apple.[11]
Since software programs available through Cydia are not required to adhere to App Store guidelines, many of them are not typical self-contained apps but instead are extensions and customizations for iOS and other apps.[12] Users install these programs for purposes including personalization and customization of the interface,[12] adding desired features and fixing annoyances,[13] and making development work on the device easier by providing access to the filesystem and command-line tools.[14][15] Many Chinese iPhone owners jailbreak their phones to install third-party Chinese character input systems because they are easier to use than Apple's.Jailbreaking also opens the possibility for using software to unofficially unlock carrier-locked iPhones so they can be used with other carriers.[17] Software-based unlocks have been available since 2008,[18] with each tool applying to a specific iPhone model and baseband version (or multiple models and versions).[19]

To put in simpler terms and not plaigarize like the other person, it is where you can get a bunch of free stuff and customize your phone to do cool things.