I like to create classes/methods with little/no/mock implementation to see how it will fit together. If there's something where I'm not sure how it works (third party API/lib I've not used before) I'll get more granular with it.

There's tooling to produce diagrams from code if someone really wants it. But either way my design phase is now usable code.

That being said, I still have to admit this rarely survives contact with actual implementation. It just feels better.