Roleplay isn't just about hanky panky obviously. There are many different types of RP; some are games and some are just a playful improv skit between friends. Of course there's more...mature...subject matter to be considered, but that's not my point. The fact of the matter is that RP can be extraordinarily helpful to a writer in determining just how a certain scenario would play out. So far I've only done this with more mature material but I'm interested in trying a few scenes from my new book Dragonspeed to get a better feel for them. Ironically I'm supposed to be writing a paper right now reviewing a play I saw two weeks ago for a teacher I'm desperately trying to get fired. I've written adult and mature material before, one screenplay in particular I've been told is excellent despite its relatively short running time of under 10min. However real "adult" material is tricky to write, especially if one wishes to get very detailed. That's why I often use roleplay transcripts when I'm writing that particular type of fiction. Its still alot of work of course. One must take a back-and-forth, shorthand transcript written entirely in the first person and convert it into prose written in, usually, the third person. The material becomes much longer; on average a finished story can be twice as long as the transcript it is based off of.
One-on-one Roleplay I find can have odd effects on a relationship between two people. Often times, if initiated with a friend, said friend may misunderstand your fictional advances as real ones, trying to then pursue a different kind of relationship. I had to close down a messenger account on one occasion due to this. Another issue is if you are actively pursuing a relationship with someone, engaging them in an RP situation can seem to trivialize the relationship. So the bottom line is that when it comes to RP, having the right buddies to do it with, regardless of what you're actually doing, is paramount.