I know this sounds little stupid , but I thought that aircraft marshalling and ground crew can make stuff more realistic and cool , for example ; someone wants to takeoff he request from the ATC to takeoff and then maybe a marshaling vehicle or a personnel comes and guide him to the way of the runway instead of checking the map every time , and another example ; someone requests a rearm then a ground crew comes to the aircraft and does and kind of animation like fixing something or anything and then it start rearming .
I know some will disagree on my opinion but its pretty cool like in night time you see the glowing sticks that they use for aircraft marshalling or the vehicle lights at the top .
sorry about my bad English :) .