I recall reading somewhere that saving citizens would somehow make your major assassinations easier, but saving all the citizens in Damascus didn't seem to do anything for me when I was running from the guards after performing the big kill. Does saving people do anything besides creating monks/vigilantes?
Edit: this refers to Assassin's Creed 1.
Best Answer
No, saving citizens doesn't do anything aside from creating monks and/or vigilante groups. However, you can then use these groups to your advantage. When you are trying to escape, you can run through a group of vigilantes to slow down the guards chasing you, giving you enough time to get to a rooftop and out of the city.
Monks can also give you a place to hide so that making an escape is simpler.
Then again, getting in huge sword fights is one of the best aspects of the game, so I always stuck around and tried to take out all the guards anyway.