Sequence diagrams are extremely useful. The only problem with UML is that it was used as a method of intellectual masturbation by people who love massive class

Sequence diagrams are extremely useful. The only problem with UML is that it was used as a method of intellectual masturbation by people who love massive class hierarchies. There's a lot of good stuff in UML, the problem is that the people who were attracted to it in the mid 90s were the same people who were poor programmers and were looking for any excuse to avoid writing code. There are the same guys who spent years building up formalisms in tools like Rational Rose and other pseudo-engineering tools. When used by good programmers to illustrate specific hard-to-reason about components of the system, it is a useful tool. Activity diagrams, sequence diagrams, use case diagrams and communication diagrams are all useful.