I understand Google has reasons why they might want to NDA their process, but from the perspective of a potential employee, being asked to sign an NDA for the interview is only a liability. Interviews can be unreasonable (and sometimes even abusive) environments, and I want to know about that before walking into that. Barring that, I want to warn people about bad interview experiences.

If people cannot talk about their interview experiences, there's no opportunity for employers to receive censure for bad interview practices.

Besides, an interview is not the SATs. If this really is the logic for the interview process, then Google interviews are even more broken than I thought.