Here are my thoughts (possible only a thought) on sex scenes: if they don't do a thang for the story, then leave them out.
No, I'm not a prude. I'm just more the type that likes to leave things up to my readers' imaginations, rather than spell everything out for them. Sometimes, the imagination is better than reality. Trust me on that one! : )
More often than not in my writing, I allude to the sex, but don't actually give detailed descriptions. It's just what works for me. Now, could I give a detailed description if needed? Hell, yeah. I just haven't come across the need to show the erotic exploits of my characters. For me, it's more fun to just let my readers figure out what Jack and Jill did when they went up the hill for the pail of water.
A perfect example of this can be found in Janet Evanovich's Stephanie Plum series. She never goes into full detail when Stephanie and Morelli have sex, or when Stephanie had sex with Ranger. I'm only through Book 8, so I'm not sure if she has sex with anybody else or not. Janet always provides the barest minimum of details with out going into extended descriptive passages. Sometimes, it's the reactions of the other characters - OMG, you had sex last night - that are more telling, rather than the actual event itself.
I know other writers/authors do things differently, because that is what works for them. Now, if I was writing some erotic story, yeah, I'd go into detail. The extensive details just don't need to be there in my current projects, even though quite a few of my characters do the big nasty.
p.s. Speaking of Janet Evanovich . . . one of the best lines ever: Holy Mary Mother of God, you were being chased by Bill Clinton, Richard Nixon, and a rabbit. I laughed for at least five minutes, and was crying by the time I was finished. Janet Evanovich is a Humor Master. It's never an entire passage, an entire book, just a sentence here or there that absolutely cracks me up.