Production data means it can change in a deployed model depending on user access/role. Think a list of locations or products. You might want this to be flexible in a live environment.
Structural typically just means not production or things that cannot be edited in a deployed model. Think the official versions list, time settings (ex-current month), any lists you don't want change and have not marked as production, etc. Pretty much anything in your settings menu on the left hand side falls under this.
Any time you create a new revision tag and sync changes structural settings/data are the things that are being updated.
Thank you @hbrink