I have written a lot of stuff about daemons and when it comes to something like a succubus, "they don't need to prep for anal, because they are magic sex monsters and always ready for sex" just works. Otherwise it depends on the "where." Like, two characters get into a hotel room together, it is easy to skip it so that they have showered and "otherwise prepped" for sex. IRL it would mess up the flow of things a bit and cause a delay, in erotica you just skipped over the boring stuff and can get right to the sex.
We don't see Indiana Jones meticulously sweeping dust off what might be clay pot fragments and meticulously recording the location and depth at which they were found, whereupon they are brought back to a basement in a university where they are effectively buried once again and never examined by anyone else because they are essentially worthless, both monetarily and scientifically. That's 90% of what archaeology is... it NOT great entertainment. Sex has a slightly higher ratio of what's great compared to what's not, but it still makes sense to skip the less fun parts for the sake of telling an entertaining story.
I have written about the prep, and people have complained. Which was surprising, since I don't normally get a lot of feedback. Maybe I'm doing anal scenes wrong.
I think for anal specifically, the prep is just kinda gross (or at the very least not explicitly sexy (unless you're into some very specific kinks, in which case more power to you!)), so skipping it on that basis might be good for the story. But there are many kinds of "prep", and there are definitely ways to make it hot. To reuse one example mentioned above, pre-sex showers offer a near endless variety of ways to raise the erotic temperature! Wet bodies, shining skin, sensuous touching, and soap making everything slippery? Oh my!
A description of anal without any preparation is kinda a deal breaker for me, similar to a description of instant vaginal without any foreplay or arousal. In my story SttT, the reader has the option of different amounts of improvised lube or spit. In my story AW, it's vaginal fluids and spit with multiple attempts and increased friction. For some characters, a lube shooter might also be a quick and easy way to prepare. That might even work when they are in a public restroom. I guess without a full enema, there might still be unwanted surprises sometimes, but that could either be overlooked or might not be enough to be an issue. If it isn't the right soap, that might make for quite a bad experience. (And water isn't a lubricant.) If condoms are used with (wrong) lubricants, it might lead to busted condoms.
Just to be clear, when I said "preparation", I wasn't talking about the general "start off slow, ease into it, then gradually intensify" that any sex act (or portrayal thereof) can benefit from. I was talking specifically about dealing with the fact that this is a hole that poop comes out of and ensuring that none of it is around to interfere with the sexy times, which is specific to anal sex.
Anything that writer includes in a story must have a purpose. 1) Show or tell the reader something about the world, characters, character growth. Something they don't already know or understand. 2) Progress the plot 3) Invoke the reader's emotion (arousing erotic scene, exciting combat scene, awe-inspiring description of nature, etc) If it doesn't do 1, 2 or 3. Keep it out of your story. Edit it out, mercilessly. And things listed here are exactly that. Also, genre conventions exist for a reason. If I watch Star Trek I don't want to be reminded that physics don't work this way or that aliens being slightly different humans is absurd. If I read porn with rough anal sex that needs no preparation and causes no injuries - I don't need to be reminded that it would be different in the real world. Of course, everyone has different boundaries of suspension of disbelief, it is why genres and subgenres exist.
Editing out everything that isn't 100% necessary may be prudent when you are publishing a complete story, but even there I feel that natural worldbuilding and minor details give life and "realism" to a story even if it is not always a Checkhov's gun. And on CHYOA where others may choose to expand upon your story OR you might choose to create multiple paths, there is no harm in adding minor stuff that will not be relevant again on one specific path.
Checkhov's Gun is caring only about 2 on my list. And I always disliked it and considered it a total bullshit idea. Story is more than its plot. Rifle on a wall can subtly inform us that some character X is a hunter. Or that rifle can be damn pretty to look at. It is not useless.
Well, see, a character being a hunter or someone who uses a deadly weapon as a mere diplay piece actually says a lot about a character. I do think that not every little detail needs to be relavent a hundred chapters down the line, but knowing how to be quiet and careful in the middle of the woods is the kind of skillset that could always be important later. Also, learning little side pieces about the characters is 100% required for optimal reader enjoyment (especially in the case of a fully published and semi-popular work).
A married celebrity or a celebrity with young children is put into a harem, but nothing about what happens to her family who just lost their wife/mom.