Diagramming is a great tool for transforming natural language into logical statements and applying rules of inference when you work on your practice sets. On a real test, it is a matter of personal preference but given the time constraints, it would be almost impossible to diagram every question that involves logical inferences, especially given that all the tests are in a digital format now. Try to read the question first and use common sense before jumping into diagramming. If the question is particularly complex or involves formal logic, then quickly diagramming the statements could be helpful.
