Many software projects /are/ big. Many of them are complicated and monolithic, written by "someone else", unrefined, and quite possibly the first thing that they managed to get working. I find UML diagrams (sequence, class etc) invaluable for understanding code like this, as a reverse engineering tool.
"An occasionally invaluable tool" is how I could describe UML diagramming.
"An occasionally invaluable tool" is how I could describe UML diagramming.