And having a strong ally also prevents people from declaring war on you. I played a very long and successful Morrocco game where I colonized large tracts of the new world and parts of Asia and was able to take on Spain and Portugal in colonial wars. All of this was because I was allied to all of North Africa for most of the game. By the time I had taken over the rest of North Africa, I was Latin tech and no longer needed strong allies. It saved me from being attacked over and over again.