One of the new features of FileMaker 12 is control over layout width. You can place fields within the layout; or place fields to the right, outside the defined width of the layout.
A field placed outside the defined width of the layout is never visible in any mode except layout mode.
However you can "go" to these fields using go to object, and with the go to field command.
I am wondering if there are practical uses of these hidden fields.
One trait I notice is that you can use the insert command to update a field's contents.
This might be useful with the new insert from URL command, for instance. You may want to get the result but may not want to flash the screen.
I also observe that if you have a script that goes to this invisible field, and puts the cursor there, you won't see it but your keystrokes will go into the field and if you commit the record, the field content will in fact be updated.