Well... what is the value of the fiction itself?
If you define it purely as entertainment, then it adds as much value as whatever you're consuming.
Right, the entertainment value can't be dismissed. I mean, I like good action scenes for the exhilaration, and for watching skilled people do something remarkable; if an action scene also moves the story or develops a character, all the better. Funny jokes don't have to move the story or develop the character, either, they can just be funny.
If you think about story progression and character development, yeah, then probably not.
I think sex scenes can and do move the story and develop characters. I just saw a great example the other night, in an episode of
New Amsterdam. Because of how prudish American network shows are, the fact that both characters were semi-dressed in the "morning after" fade-in didn't tell me whether they'd done it or not. It was up in the air whether they would do the deed or not, and it was vital to know for the progression of both characters, one of whom is the show's lead. As it happened, it was cleared up a moment later, so I wasn't pulling my hair out for long. But that moment of being unsure what had just happened, whether they'd slept together or just next to each other, made me crazy, because it was important to know.
Just had a sudden thought:
The Americans had a lot of sex scenes, and I can't think of a single one that didn't move the plot or develop the characters.