Sync while using a custom passphrase
Sign in to your Chromebook.
Enter your passphrase.
Click the status area, where your account picture appears.
In the "People" section, click Advanced sync settings.
In the box that appears, choose what you want to sync:
To sync everything, select Sync everything from the dropdown menu.
To choose specific items to sync, select Choose what to sync from the dropdown menu, then check the items you want to sync.
Note: You'll need to enter the passphrase on each Chromebook you want to sync. If you've forgotten your passphrase, go to Google Dashboard and remove sync information from your Google Account, then set up sync again.
Why Would I do this?
hands-on experience shows that the default is only to encrypt the password and not necessarily the synced user data. If you put in custom password you can select to encrypt all your sync data... with your password.