iTunes does not provide an menu option for enabling or disabling backups, but you can manually update the iTunes preference file to do the trick. There is a preference called “DeviceBackupsDisabled”. If you do decide to disable backups on a regular basis, note that MOST of your data will automatically be synced to your phone — but your Text Messages are not synced outside of the normal iTunes Backup process.

To disable backups:

1. Quit iTunes
2. Open Terminal.app
3. defaults write com.apple.iTunes DeviceBackupsDisabled -bool true
4. Open iTunes
5. Sync

To enable backups:

1. Quit iTunes
2. Open Terminal.app
3. defaults write com.apple.iTunes DeviceBackupsDisabled -bool false
4. Open iTunes
5. Sync

Enjoy