Whenever the test is to see what clarifying questions they'll ask.

Give a dev in an interview setting a vague task that needs refining before it can be meaningfully attempted, and 95% of them will just plough in and start designing / writing code.

FWIW, I don't personally like these sorts of questions in interviews, as the situation is very different to reality (and therefore I don't believe it's a true reflection of what questions a user may ask in a work environment.) They are *very* common however, and a lot of devs don't seem to be aware.