"Should I backup my iPhone before jailbreak?"
The answer is definitely yes. Since long-waited untethered evasi0n iOS 7 jailbreak is available, you may want to jailbreak your iPhone running iOS 7. However, just as what could happen the to iOS 6 jailbreak, you could suffer data loss during or after iOS 7 jailbreak, such as losing iPhone photos, contacts, messages, videos, call history and more. Therefore, you should backup iPhone on computer before jailbreak, no matter whether it is for iOS 6 jailbreak or for iOS 8 jailbreak.
We do not recommend you to backup iPhone files with iTunes, since the backed up files will be a series of SQLITEDB files, which are unreadable and difficult to get necessary info from, and in many cases iTunes fails to backup all of your iPhone data. iCloud is not a very good option because it only gets 5 GB free space and it easily gets attacked by some ill-disposed hackers. To 100% secure your iPhone data, we advise you to backup iPhone data to your computer with iPhone Data Recovery before you try to jailbreak the device.
iPhone Data Recovery can help to transfer all data including pictures, contacts, videos, messages, notes, Safari bookmarks and more items up to 12 types to your local computer running Windows i8.1/8/7/XP/Vista. It will never fully supports iPhone 5S, iPhone 5C, iPhone 5, iPhone 4S, iPhone 4, iPhone 3GS. If you have a Mac on OS X 10.9/10.8/10.7/10.6, go to the Mac version, iPhone Data Software for Mac.
All text content like call history, text messages, iMessages, WhatsApp messages, calendars, notes can be backed up in the formats of .txt, .xls, .xml, contacts into vCard/VCF files, and media content in their original formats. So that you can view, edit, transfer back to iPhone after jailbreak and do more. No damage to all the files.
Now download and install iPhone Data Recovery on your computer and then follow the guides below to backup iPhone on Windows before jailbreak.
If you have synced your iPhone with iTunes once, iPhone Data Recovery can also help to extract data from the unreadable iTunes backup files and backup all of them in readable formats on your computer hard drive. Select "Recover Data from iTunes Backup File" on the software's interface and do as the wizard shows you.
"I didn't backup my iPhone before jailbreak and it deleted all my data. Help."
Backing up iPhone data to PC before jailbreak can avoid data loss forever. If you forget to backup your device, you can easily get back all lost contents as long as you never put any new items to overwrite the space. Since we have dedicated the method to recover lost data after iPhone jailbreak in the article Any iPhone Data Recovery Tool, you can go to check it now.