This video comes in handy for those who own a Jailbroken iDevice on previous firmware (for example, iOS 9.1, iOS 9.0.2 or iOS 8.x) and the phone started working pretty slow due to the installed tweaks and temporary files. In this case, the best bet would be to restore the device, but iTunes will automatically update it to the latest version (iOS 9.3.2 as for now), therefore, you will lose the Jailbreak.
So what can you do?
SemiRestore application is the best thing in this case. It offers the ability to restore the device in less than 2-3 minutes, without removing Cydia (without losing the Jailbreak) and without updating the iOS version. Although Cydia is not removed, all tweaks and modifications are wiped out and the phone gets its fresh state again. The application removes every setting, turning the phone exactly to Factory Settings, but leaving Cydia and the Jailbreak base files untouched.
Semirestore 9 is compatible with all iDevices, all firmware versions starting from iOS 5.0 to iOS 9.1 and requires only OpenSSH to be installed in Cydia (it is free).
Semirestore can be used on Linux, Windows or OS X with no issue.
On OS X, it requires you to disable Gate Keeper (shown in the tutorial) and to install 2 homebrew packs in Terminal (shown as well).
Our tests shown the app is quite stable and safe to be used. A backup would still be recommended. JUST. IN. CASE.