The Max. Expansion settings determine how much of the graph to display. The default depth value is 2--this ensures that only functions that directly call (or are directly called by) are shown in the graph. If this value were set to 3, for example, then functions that call a function that calls the function being browsed would also be displayed.
The breadth value has a default value of 40, and sets how many functions are displayed at each level of the graph.