It allows you to remove the jailbreak from your jailbroken device and return it to stock Apple i OS software without the need of restoring (updating) it.
There are several tools such as i LEX RAT, a command line tool, and Semi-Restore, a desktop tool that allow you to restore your jailbroken device without losing the jailbreak.
Since restoring your device would mean installing the latest i OS software update, Cydia Impactor gives you the option to remain at the i OS software update that can be jailbroken, which can be very valuable.
saurik also has explained how the tool works: Impactor uses the firmware archives provided by Apple for its “over the air” update feature.
Automatically extract and restore Whats App messages from i Tunes backup files particularly useful when your device is broken, lost or i Tunes can't recognize it.
i OS 8.0 - 8.3i OS 7.1 - 7.1.2i OS 7.0 - 7.0.6i OS 6.1.3 - 6.1.6i OS 6.0.0 - 6.1.2i OS 5.1.1 or 5.0.1i OS 4.3.3 and Older Community Q&A Jailbreaking your i Pod Touch will allow you to tweak your device to suit your preferences.
You can install new themes, apps that Apple doesn’t allow on their store, and much more.
It allows you to recover i Phone/i Pad/i Pod data including text messages, contacts, photos, videos, notes, Whats App and more without paying.
Whenever you encounter data loss due to accidental deletion, i OS update, jailbreak failure, or i Devices get lost, stolen, broken or locked, Free i Phone Recovery software is always your best choice to rescue important data from i Phone, i Tunes or i Cloud backup.