I do not consider the Mistress-slave dynamic to be a roleplay in the sense that we simply "pretend" at conventional role reversal. Rather, I view these roles as a true expression of the power exchange between my clients and myself, during the playing of a scene as well as in our interactions beforehand and afterwards. It is how I expect those who submit to me to treat me at all times. Now, that does not mean you need to get on your knees as soon as you see me. It's about according me a level of deference, respect and attentiveness that goes above and beyond that of a service provider.
As for roleplaying, I get a kick out of acting out creative scenarios as a starting point for a scene. Yet what I find typically happens is the scene eventually evolves out of the specific roleplay and back into the overarching Mistress-slave dynamic. For me, this is the fundamental and defining force which underlies all of my interactions with my submissives.