I don't really think there is much difference between being descriptive and roleplay. You're not physically there, all you can do is to describe actions and guess what a possible reaction could be, describing it as well. That's already roleplay, even if you just 'play' your own self. You can add fantasy, sci-fy, a different background story, change your hair color ... or nothing at all. What you're doing remains the same. Two or more people use nothing but the written word to create an exciting experience. A story, set up by more than just one mind.
I'd be a rather extreme example of course, packed with everything from sci-fy to fantasy. And still I meet a lot of people who're completely casual, vanilla if you like.
The photographer who never did anything but to use his 'job' to hook up nice girls ... Let's meet him, maybe to ask him to take some pictures from my newly collared girl. He wouldn't know, or expect anything unusual to happen, all he does is his thing, describing how he takes the first shots. I could just keep things there, have a regular encounter, never mentioning anything unnatural. But that wouldn't be me, right? So I'll do something unexpected, something this photographer has never seen before ... He may be surprised, shocked, maybe even scared ... but also excited, intrigued ... and then I'll give him something he'll seriously never forget.
Was he real? His job? His hair color? Who cares?
It's been a fascinating evening, three people sharing about 5 hours packed with wonderful, exciting descriptive play. That's what I am here for.