Restrictions under Benefits Enrollment?

I'm looking for more information / documentation on how to use the Restrictions section under the Enrollment train stop. I've searched both the Implementing and Using Ben guides and the Imp has a bunch about cert restrictions, but not the enrollment restrictions. I'm trying to understand the purpose and when I'd use it. Does anyone have any documentation on this or even better, some specific scenarios where this has come into play for you? I think if I had a few real-world examples of using it, that would be very helpful! Thanks in advance.