It turns them into animals, if you enable free will. And the sex can last a while, I’d recommend clicking 3, to speed it up. You could try cancelling it, but they might get unhappy if I do that.

If you go to a birthday party, you’ll see Sims you can’t control, having sex.

Yeah, you can disable the sex free will. But it’s kind of funny. They might miss work too.

They can even have sex through a coffee table. On and through it. I found that out, because they had sex by themselves.