[alexdm0]

CGamesPlay and TuringTest are both right, the gravity and springs model allows us to neatly show the data. These calculations take time and for bigger systems one might have to wait tens of seconds for it to settle. For smaller systems it's perfectly feasible to do this before rendering. To make sure the user sees a result instantly and to promote the interactivity the movement is shown.

I'd like to add that vis allows you to store the positions and use these for the next time someone views the graph. That way it may take some time to settle initially but is loaded nearly instantly the next time you, or another user, views it!