I was at an erotica writing workshop recently, and one of the women running the panel on characterization said that one of the scenes she likes to write is the "celebration" scene. That's what she called it. The whole "We've been through a terrible time and survived. Let's celebrate... by fucking!"
I asked her about that. Shouldn't every scene move the story forward? She was adamant that a celebratory scene was acceptable on its own terms, that it didn't need to advance the plot or characterization in any way.
I disagreed, and I still do. I find the "celebration" scenes at the end of Star Wars and Return of the Jedi rather boring (although My Little Pony's send-up is cute) in that they don't really wrap up anything. "The Heroes lived happily ever after" is all fine and dandy, but the throne room sequence goes on and on.
And I think it's especially true of erotica. The whole point of erotica is to get the characters to reveal something important of themselves in the bedroom, to realize their own self-knowledge or their knowledge of the other, or to advance a personal, perhaps even inimical agenda.
To paraphrase a common writer's saying, "They fucked and it was good" is just an anecdote. "They fucked and it was good because she overcame her fear of hurting him" has a plot.