I work with non-distributed (ish) systems, and I use watered down class diagrams much more often than sequence diagrams.

But even when I was working on more distributed systems, I found more value in state machines and simplified class diagrams, actually. I think most cases where you're using a sequence diagram, a state machine is a better tool. Both for thought, and for implementation. Surfacing implicit state machines can require some extra upfront design, but if you have a non-trivial amount of states, it's pretty much guaranteed to be worth it.