None, in fact. I never like to use any kind of representation out of pure imagination for RPG. I describe the scene, players visualize it, and I try to be as precise as possible (anyway I have the last word
).
Seriously, the idea behind it is that in the middle of an action, things are always a bit confusing and always on the move. Papers and pencils are taking out fluidity. Of course, they are useful when planing an action if you have time to plan. I use them often in case of planing. The problem with this is that the action often evolves in a different way or too quickly. If you take time to plan, oops, you're dead!!
As GM I keep tracks of what my players are doing and I rely on everyone's honesty (usually it works). In my experience, papers and pencils make things more confusing as they are often contradicting your authority as GM. When a player is obviously not playing by the rules he has a strange tendancy to take a leak on minefields and to run bare hands in front of T-72's companies (giving a nice warning to his fellow honest players
).