This is another of those subjects that you get people solidly on both sides of and facing the middle. Can you have extraneous sex in erotica? Some people claim that's impossible. Some claim it is. I am with the latter, and I'll tell you why.
This has nothing to do with how hot you like your erotica. It has nothing to do with how much sex you like to read about. It has to do with the appropriateness of the scene.
But wait... We're talking erotica, right? Erotica is about sex. It's about arousing the readers.
Erotica does entail arousal. I won't deny it, but that's not all there is to erotica. If all you have are sex scenes strung together, you either have porn or a "retrospective study of the sexual animal, human." Call it what it is and be done with it.
Erotica consists of a solid plotline and characterization tying it all together. There is a REASON for the sex. There is a connection between characters and the sex that happens.
Is the book about the sexual journey or exploration of a character? Moral or social effects of it...or conversely, how moral and social culture affects or complicates the sex? Religious pursuits? Is it erotic romance, and we're seeing the relationship bloom? Finding yourself sexually? There are a lot of possibilities.
As in any book that is solidly built on plotline and characterization (no matter WHAT genre you're talking), every scene in the book should serve the purpose of advancing the plot/subplot/coplots and/or establishing characterization or the growth thereof. If it doesn't do that, it doesn't belong in the book, in the first place. It's going to feel slapped in, and the reader is likely to feel it and react negatively to it, whether they can name why they do or not.
Also, a decent plotline doesn't get repetative...and decent characters don't spend the entire book arguing the same argument or making the same dumb mistake. Otherwise, why would anyone care to read it?
What does that have to do with the price of beer? Not much, but it does mean, if you are just doing it to do it and do it and do it, you're going to bore the HELL out of your readers. Is that really what you want to do? I hope not.
So... From my point of view, as both an author of and reader of erotic genres of all sorts, if you don't have a reason for the scene, remove it, no matter what it is. If it feels slapped in, tie it in or remove it. If you're not covering fresh territory (and I DON'T just mean sexual positions here), drop it.
It's better to have less but powerful than a glut of something ho-hum.