One Stop Erotica Shop!

I am wondering what does a person get out of writing erotica? I have been writing it since I got to college romance since I was 15 or 16. Frankly I just do it because I wonder what reaction does it get from people one and second because I have an extensive knowledge of sexual behavior so it suits me as a hobby. I have something that I am unclear about. Fisting, how many people actually do it. Role playing why become fixated in just one role when a variety keeps not only ones interest and imagination working having just one role to like makes it an obsession. Last can S&M really feel good. After being hit with a belt maybe once or twice when I was a kid I am wondering what is the appeal.