I just realized something looking at a group table in a tournament. -I was wondering how come there are so many black wins in the lower triangle, and so many white wins in the upper triangle?
then it hit me: in every game in the lower triangle the black player is higher rated, and in upper triangle the white is higher rated. which also means: in every game with a black dot in the upper triangle the lower rated player won, and vice versa in the lower triangle.
so, you can spot the upsets immediately from the 'wrong coloured' dot which will stick out like a sore thumb, and get a good idea how the group is going for different players, just with a one quick glance.