Are Declarations of Friendship worth it?
If you make a Declaration of Friendship, there are many bad points:
- Your friend will regularly ask you for money or Resources.
- It will negatively affect your relationship with your friend's enemies
- You cannot Denounce your friend or Declare War on him or her without incurring diplomatic penalties with all other Civilizations.
- If you do anything to annoy your friend, e.g. not agreeing to his/her regular demands for money, then he/she will usually Denounce you and this will negatively affect your relationship with all other Civilizations ("Your Friends found reason to Denounce you!")
There don't seem to be many good points: 1) it will positively affect your relationship with your friend's friends
So, is it worth publicly Declaring Friendship at all?
Friends can be useful in two situations:
(1) If your friend is powerful, it may deter one of your close neighbours from attacking you, both if they're your friend's friend, and if your friend is stronger than them. In a similar vein, if you made an enemy, and can DOF with someone who lives more closely to said enemy, the enemy is more likely to butcher your new-found friend first (and the demanded resources allow you to somewhat fight a proxy war).
(2) If you want others to declare war on you so that they may bleed themselves dry on that citadel you built on a choke point, or because you don't want to look like a warmonger to everyone, a DOF with their sworn enemy helps pushing them over the edge.
A declaration of friendship is needed to make a research agreement with a civ, so if you are pursuing a tech victory, they can be worth it, too.
The Gods and Kings expansion, if you have it, added positive modifiers when you befriend two civs that are friends with each other, which of course also is a welcome extra bonus.