Jailbreaking an i Phone, despite voiding your warranty, will not prevent you from continuing to use all the apps you've bought through the i Tunes App Store.
Rather, the process adds an alternative app store, Cydia, to your phone, which works alongside the official App Store.
Apps like facebook, quora etc dont need to be backup up as they hardly contain any important user data.
Now if u use itunes to backup the app data, you only have the option to restore the whole backup, not the specific parts/apps you want.
Often we have to upgrade, re-jailbreak and re-install all the previous apps, because after every 2 or 3 months new i OS update comes.
With the new update, a new jailbreak utility also comes.
They are always eager to get the updates of these latest i OS so that they can also upgrade their jailbroken i Phones. It then necessitates the respective user to look for a way of keeping and recovering this data. Right click on this device and select the “Back Up Now” button. Additionally, if you want to ensure more security for your data, you can select “Encrypt i Phone Backup” option.