Each RPC will have randomized traits for every playthrough that can be a pro or con in different situations. The one I saw, a woman named Maria, had a temperament called "Hair Trigger" that made her more likely to ignore orders and shoot at the first possible opportunity. In combat, this could lead to a scenario where you're trying to move her to cover, but she ends up taking pot shots and leaving herself open to return fire. The different temperaments that characters have will actually progress and change over the course of your playthrough, so Maria might grow out of being quick to pull the trigger.
There are even various allegiances that some characters will have to others. Using Maria for another example, she had a lover somewhere in Chicago that she was loyal to. While she was willing to do grunt work for Al, the possibility of running into her lover in combat could result in her either running from the fight or the two joining forces and taking everyone else out. Those types of emergent experiences are a part of what Romero hopes will make Empire of Sin a game players will return to time and again.