The highlighted node on the graph (indicated by a red box) changes to reflect your selection in the list. Also, by selecting a node on the graph, the corresponding list item will be highlighted. This is useful if you have a large graph, for the text on the nodes of the graph is impossible to read when the graph is fully displayed. You could zoom in the graph to read the nodes, however, it is sometimes important to know what a node represents while maintaining the context of the graphical representation.