ChetOS.net

If you change a graph traversal algorithm from stack-based to queue-based, you change it from depth-first to breadth-first.

Breadth-first is useful when you want to process siblings before processing their children.  Depth-first traversal processes as deep as it can before backtracking.

Interesting note: although this is clearly a use for recursion, either method can be implemented iteratively to save space on the stack (and sidestep potential stack overflow issues when there are many nodes).