Well, there would be three use cases.
- Admin option to allow for users to have the ability to turn on/of navigation menu
- User option to select a personal default navigation selection
- System will deliver the personal option of the navigation selection overriding the website default setting.
I know this is not a formal use case, actors, goal, system, and flow, but it is a simple change.
Does it make sense, or do you need more detail on the requested feature?