It depends on the story I'm trying to tell. I try to keep things real, but reality is pretty fucked up. On the smut side of things, I'll toe the line between the two, but I at least try to make the fantasy more realistic. For example, one of the tropes I use is the guy who can cum and cum again. It all depends on age and health and experience, but in my stories he usually gets a first shot and quick recovery. Why? When things are really erotic for guys, they can recover their stamina faster but will hit a wall before too long. Depending on the character they get maybe 2 shots before they need a cooldown.
It's why a lot of my stories with multiple victims usually have a lesbian scene after the first round or two of attacks, to give the guys a show and humiliate the women even further. If it's just one victim, that's where the forced orgasm scene comes in.
As far as details go, I try to get everything right and make things realistic, but not everything needs to be shown or said. Especially if it's something we've seen before. For example, in the Pharma series Morgana and Drew are a married couple trying for a kid. Did I go into detail the first time they sex "on screen"? Yes. Do I need to be that explicit each and every time the married couple fucks? No. To me, it's like the scene in the Western where the main character learns how to ride a horse. Now that we've shown them handling the horse, do we need to show them handling said horse each time they enter a new scene? Not unless it's important, and if that's the case something else happened. If there's a new spin on their fucking, like she's thinking of Tommy while her husband plows her, I'll cover that.
For me it's the non-porn stuff where I try to stay the most realistic. Call me crazy, but I always get torn out of a story if something is off that I know is off. Like, every time we hear a story about a chick who fucked a guy with a big dick and now she's "as loose as a bathrobe sleeve." No, that's not how a vagina works, you just have a small pecker and don't know what you're doing. It's not as bad with a non-porn detail but it still happens. I'm a bit of a car guy, so when I hear about a BMW driver using a turn signal, I immediately know it's fake because no BMW driver in the history of driving has ever used a fucking turn signal. Or if a story takes place in a certain time, I try to get the location and time accurate. In Bob and the Mean Girls, the story takes place in 1995. No one had cell phones but beepers were popular. People would send pager codes all the time in short hand, like "Here's my code for call me at home" or "Don't come home, 50's at the door" or "Yo, your bitch be crazy, she just tried microwaving the cat again." I try to use accurate story elements when I write, but will take liberties for a good story. A good story is better than a real story but if can be real and good, make it both. I'll spend way too much time researching something like how a dialect from Eastern Australia differs from Gold Coast or the rental market in Melbourne's harbor to get that part right so I can maybe have a little leeway if the guy drugs and screws his flatmate's girl because he's behind on the rent.
The same goes for Sci-fi and fantasy stories, too. I have to make you feel that it's a real world, that at least this part of the world is consistent with itself. Is it this world? Probably not. But it's world has to be consistent. Writing a story about pack of raping, rampaging Orcs running through downtown LA and no one bats an eye is crazy, but if this was an every other day occurrence in this world, that's a different story. If the story takes place in this world but there's a handful of people with mental powers to dive into minds and control people, why is this still a secret and rare thing? I have to make that part believable.