It's great for including diagrams with your code, and is great for sequence diagrams, but I wouldn't use it for more complex communication diagrams where it starts to creak a bit.
Yeah, I think this is a convenience tool to make the easy task easier. The complicated task is still probably pretty complicated.
I've mostly been using it for sequence diagrams, and yes, it's is great for that! I haven't tried modeling anything very complex as of yet, but I'll see how that goes.