When output_format is nodes_and_edges, GraphGen output is relational (rows and columns) instead of the typical URL you get when output_format is one of the visualization types. Relational output is particularly useful if you want to take advantage of some of the graph calculations performed by GraphGen. E.g. if you create a graph with 30 modularity groupings and want a list of nodes w/ modularity index, this is easily accomplished with nodes_and_edges. You can CTAS the output for further analysis.
Interesting option, never heard of it...
I don't have access to an Aster system right now, but your quote seems to imply you can simply set the output_format to 'nodes_and_edges'. If this return a result set you can materialize it using Create Table As.
So what happens when you try that?