By default iTunes will automatically sync any iPhone, iPad, iPod, or iPod touch when any of these devices is attached to your computer using a USB sync cable. If you'd prefer to manually sync your iOS Device you can. Here's how: launch iTunes, open iTunes Preferences, select the Device tab, and check the box next to Prevent iPods, iPhones, and iPads from syncing automatically.
Once this is done you'll have to manually sync your iOS device after plugging it into your Mac. Keep this in mind since without manually performing a sync periodically you won't have any backups, etc.
This tip is mostly useful if you have more than one Mac. Generally, you usually only sync to one primary computer running iTunes. If you have a secondary computer that you don't sync with then turning this feature on (it is off by default) will prevent any sync activities from happening automatically for any reason on the secondary computer.
