Supernatural hasn't spent a lot of time on relationship stories, and this is a really nice mechanism to do that without imposing that on the forward momentum of these other stories that we're telling. In the writers' room we tend to say, "We're never going to be able to give a hell or Purgatory as good as people's imaginations," so the instinct is normally not to go there. But, we went the other way this year and said, "We are going to go there," because there's a really, really strong character thing going on down there.
