Actually it can have some impact on gameplay.
In a game with a world modelled after real life, when we look at things such as walls, doors, windows, trucks and more that we've all seen in real life we tend to use their apparent size to determine distance and to estimate what size other things in the game are going to be relative the things we've seen.
For instance, looking through a doorway, one would assume that aiming approximately 1/4 from the top would be pretty close to the head of someone walking through the door. In the game taking that shot would be over the head of someone walking through the doorway.
Same thing would apply to windows and walls. From a distance you could aim at the corner and approximate the height of a man compared to the size of bricks and how hight the windows are, but again, if the scale is different between the world and the characters, things become strange.
Now that I think about it this scale inconsistency might be the reason why I've always felt that the kill distances where a lot longer than what the game said.