[h0l0cube]

I have absolutely used it for designing before building complex things and documenting complex things after they've been built. At the design phase, I find it's useful to iterate on high-level UML to anticipate the architectural challenges that lay ahead vs iterating on implementation when I've already found myself in the weeds. If you peruse AWS documentation you'll see UML diagrams of all kinds right through it. And you're probably very familiar with sequence diagrams if you do anything network or concurrency related.