Dropbox is an easy and free way to get secure online backups and file sync across all your computers and devices.
If you don't want to enable or use Dropbox from within the apps, you don't have to.
But if you do, it's as easy as linking your Dropbox account from within the app. Once you've done that, any backups you create will be uploaded to your Dropbox automatically. If you ever lose your iPad or suffer data loss, you can import your old backup file. The apps will automatically download the backup file, so you don't need to copy anything around manually.
While iTunes does create backups of all your apps and data when you sync, this allows for a more fine-grained backup process for these apps in particular.
The backup format is compatible between the three apps, so you can do some interesting things if you want. For example, you might want to write drafts while traveling or commuting on your iPhone. When you're done you could create a backup of the last few entries (or just the one entry if that's all you wanted to sync) and then open your iPad and import that backup file.
The things you wrote on your iPhone (and any photos you added) will now be on your iPad. You can tidy up the draft from there and take solace in the fact that all your writing is in one place.