If you don't understand your object graph, then maintaining a large codebase is going to become very difficult. You'll get questions like 'who is responsible fo

If you don't understand your object graph, then maintaining a large codebase is going to become very difficult. You'll get questions like 'who is responsible for updating this object' or 'who is responsible for notifying when X happens', or 'why does every object talk to every other object', or 'why does it work very slowly when there's a large number of objects'