Have you ever wanted to be someone or something else? Why don't we count hands for those who haven't... nope, I'm not seeing very many. For those with an open mind and a reasonable amount of imagination, roleplaying in the bedroom opens doors to pleasure that could be difficult if not impossible to achieve without this very enjoyable practice.
There are many different types of bedroom roleplaying, and the actual limits only exist within the minds and comfort levels of those involved.
Several types include:
Doctor/Nurse, Priest/Nun, Jailer/Prisoner: The classic authority figure scenario. When one member has professional or situational authority over the other and utilizes it to coerce/convince/somewhat force the other into sexual activity. This is good for those who want to dip into dominant/submissive roles without the idea of B&D that tends to go hand in hand with D/s.
Alternate persona: This is our personal favorite, because it allows you to shuck off your actual personality and create another that could be totally willing to engage in activity that you normally would not do. I don't mean for people to do it unwisely, but as an exploration method it can't be beaten. Participants can merely refer to themselves or their partners by another name or they can go as far as to create an entire persona, complete with as simple or complicated a back story as you wish.
Animalistic: some call themselves furries, others insist that they're just in touch with their feral side, but most agree: they're really not reenacting bestiality. They're exploring their sexuality, which is perfectly OK as long as everyone involved consents. I have never personally engaged in this type of bedroom RP, but I don't think I'd automatically turn it down if it were offered. Animalistic roleplaying generally doesn't care about relative "species", though I hear that some self proclaimed furries may look down on those who identify with animals they consider to be beneath their chosen persona.
These three are by no means an exhaustive list. If you can imagine it, you can tell someone else and they might just let themselves into your fantasy world for a little while.
Roleplaying is more satisfying with a partner or partners who are aware of what's going on in your mind. While it's entirely possible to roleplay on your own, it's so much better when all involved are following the chosen scenario.
It gives variety to those who feel their sex life is dull and unexciting.
It allows couples (or trios, quads, moresomes) to grow closer by bonding through imagination.
It doesn't really cost anything unless you desire props, special clothing, or other sensual appliances.
Roleplaying: not just for dorks anymore.