@Sam the flow of the sig is making sure that it is all going the same direction. If you think back to when you were a kid, when you would colour in an image you would colour it all in the same direction. If you look at my sig for example, everything is going from right to left. Another good example I can think of if he will let me use it is Aido's, it goes from the bottom left to the top right of the render. Essentially you want the background to be going the same way as the render.