As I'd heard it, the algorithmic piece would only be used in the case where they would have normally (with the crazy questions process) passed over the candidate.

One of the pieces of culture at Google is that everyone wants to make sure everyone there is smart, so they basically send away anyone they have doubts about, even if the person's actually genius-level. The test would be a way to, without subjectivity, indicate some cultural fit that the interviewer by bad luck missed.