The one unit that i never really see the need for is the spy. Province loyalty can easily be maintained by a small garrison of peasents, with nice buildings like churchs to keep every one happy.

In my experience, with the ease of building a guard tower, sending a spy abroad is just cruel to his family. It would be neat to be able to ferret out secrets, or incite a rebellion, but they just die.

I know that some people swear by spies, so i ask for any tips or suggestions to their use.