I'm confused. Are you saying that you never heard of a fiction writer outlining his work? Yesterday, I heard a CSpan interview with John Grisholm. He said he has never written a fiction book without first completing an extremely detailed outline.
NO. I am saying I have never heard of an AGENT REQUESTING such a thing. Obviously some agents do, since this asker is asking about it -- but I personally have never asked for such a thing, nor worked for an agency that required such a thing, and would have no idea what an agent who WOULD would be looking for.
Writers might use outlines to write -- or they might use flash cards or family trees or 150 yellow pads of paper or audio tapes -- but why would I want to see that as an agent? I care about the finished product.
Nonfiction is another story, I realize that many agents sell nonfiction mss on proposal, so of course they want an outline of some sort. But the asker was asking about fiction.