I guess I could run a game with some high poly objects. But in order to not exclude everyone that aren't running a new awesome computer, it's preferable to stick to the default poly count. A 75000 polygon chopper might be good for a cg movie, but is just bad optimization for a comper game. It doesn't need to have the bolts and screws modeled. Much rather use the high poly model to bake a normal map on a optimized low poly model and use that in game.