I usually bribe people ito wars with others in order to prevent ending up in war with them myself.
If i declare war, i very often had the enemy buy allies against me. So now, before i go to war with a civ, i will buy the whole world against him.
Also did i think it might be possible the AI wont start a war when it is already at war with many enemies, so the more enemies they have the better. But dunno if that is true.
The above 3 mentioned things i have never noticed being needed.
mutual protection pacts i never do.