I'll often use sequence diagrams or entity relationship diagrams when I need to explain how a piece of code works (or even just visualize it for myself). I don't tend to be very pedantically correct about it, but having a picture makes it a lot easier to follow how different pieces fit together. I generally leave out a lot of the less important details when doing this.
I wouldn't generally use it to design code that hadn't been written yet. There's a lot you only discover once you get something working, and that needs to inform the design.
I wouldn't generally use it to design code that hadn't been written yet. There's a lot you only discover once you get something working, and that needs to inform the design.