Sequence diagrams are quite useful, static diagrams, not so much. I only find myself drawing them if I&#x27;m trying to do a necropsy to figure out hosed up object relationships.<p>The other useful diagram tfa doesn&#x27;t cover is the finite state machine diagram. Handy, plus, they look cool.<p>As an aside, I find it&#x27;s much, much easier to do with pen &amp; paper than in any tool i&#x27;ve ever used (looking at you omnigraffle &amp; visio!)