Graphviz Visual Editor Q2: When I select “Fit graph to available area” I don’t see any effect on the graphic window. Is there something else I have to do as well?
No. What is the problem? Does the graph never fit to the available are or does it always fit regardless?
Try also the 1:1 button in the toolbar: 
and then toggle “Fit graph to available area” and you will probably notice a difference. The 
button has the same effect when the “Fit graph to available area” option is off.