Country_options / state_options?

I stumbled upon a very undocumented feature:
country_options and state_options form helpers

I dont see anyone using those in numerous address forms tutorials and
The first thing that comes to mind is that its probably more efficient
to create country and states tables and use foreign keys rather than
storing the value for every row…

Maybe it is very obvious, but for someone as unexperienced as i am, it
is not.

Could anyone point me to a good example using those?