This tool is dubbed the Cydia Impactor and it basically “unjailbreaks” your iOS device. This might come in handy if you’re planning on selling off your iOS device while still retaining the ability to jailbreak, or if you have run into any issues with the jailbreak and you want to start again with a fresh install without having to go through the jailbreak process.
While we haven’t taken it for a spin ourselves, the folks at iClarified has described the process as, “All files on your device that have been modified or otherwise destroyed are downloaded directly from Apple. In a series of carefully calculated file migrations, all new files are moved to the user partition, and all system data is moved back to the system partition.”
It’s an interesting concept and if you’d like to check it out for yourself, you should be able to find the package in Cydia, assuming that you have jailbroken your device already.