Design notations, such as UML, and long-lived design documents have at least one advantage: if you're overseeing the work of a software team, they are tangible, auditable deliverables that allow you to assess the team's design practices. You may, however, find this assessment more difficult to make if you're dealing with an agile team. For one thing, there is a widespread perception that agile approaches frown on documentation and prefer direct communication -- which leaves no written trace.