One of the most common (and obvious) recommendation before hacking the iPhone is to backup the iPhone so that if things go horribly wrong you can at least restore your iPhone to avoid losing any of your settings such as sound settings, widget settings, certain network settings, and other preferences and information such as text messages, notes, call history contact favorites etc.
Apple recently published a must-read Knowledge Base Article from iPhone and iPod Touch owners which brings in a lot of clarity with regards to the difference between backups and syncing as well as how to create a backup, restore from a backup and deleting a backup.
Here is what Apple has to say about the difference between Syncing and Backups:
“You can use iTunes to sync content on your computer (such as music, podcasts, videos, ringtones1, photos, email account settings, contacts, calendars, and bookmarks) with your iPhone or iPod touch. Syncing makes sure this content is the same on your iPhone or iPod touch and computer.
You can also use iTunes to create a backup of settings and certain other information on your iPhone or iPod touch to use in case you want to restore the software on your iPhone or iPod touch or transfer this information to a different device. Backup information includes information such as mail settings, text messages, notes, call history, contact favorites, sound settings, widget settings, certain network settings, and other preferences.”
To get more details on the procedure to follow to create a backup, restore from a backup and deleting a backup, follow this link.