Hi Brian,
Well the use case is simple when you use Joomla in a intensive production flow...
Example :
I develop a lot of websites based on the same initial configuration... So to save time I have a basic pre-configured installation that I replicate for each new client that choose a certain kind of website.
This the base has a lot of options and also a default multilingual configuration (I live in Belgium so it is needed but it could be the case for a lot of people living in Canada, Switzerland and other countries where many different languages are speaked depending the part of the country they live).
Then I adapt the configuration depending on the options they chose (I can remove modules, a blog or even a language if they don't need it).
When I dot this I unpublish the elements they don't need and put them in the trash (I never completely delete them because clients are so mind changing that if I delete something you can be sure that the next day they will ask me to put it back).
Based on that experience and the kind of use I do with Joomla, I'm facing the problem that even if a disable a language, the menu I created for it is still visible everywhere in the admin... It is the same problem for a sub menu for a blog or any king of menu you can create and for any kind of reason you don't need for a certain time..
So my clients can always see things that are not "activated" in their websites and they can make mistakes too when linking a module to a page if menus not in use are still visible...
Well that's it for the example...
I'm pretty sure many people would find usefulness of this upgrade... think about people adapting their websites for events or temporal functionalities... be able to unpublish a menu for a certain time can be usefull..