What’s the deal with character questionnaires?

Character worksheets or questions or interviews are pretty commonly recommended to develop characters.  They’ve always had me scratching my head.  I’ve never really understand the purpose—and this is an actual example from one of them—of identifying the time a character drinks tea every morning.

Or even that logic that I’ve heard that doesn’t make sense to me: “You have to know every detail even if it’s not in the story.”

I’d look at it and rather go off and write the story and find out, then do boring, and what would be to me very mechanical, questions.

I don’t even know what my main character’s favorite color is.  Her least favorite color is yellow, but then, that’s the least favorite color of every character in the story because the aliens they’re dealing with are yellow. Ain’t no one liking yellow.

But I also trust that if I need to know that fact, it’ll show up in the story when it needs to be there.