I actively include 'smut' into my RPs, as many of them involve relationships and romance and a lot of the focus is on those areas (while including an overall plot line). I'll be honest, a lot of why I do it is because I straight up enjoy it. It's fun. It's creative. And it can get kind of sexy. I'm not ashamed of that. But another part of why I do it is because personally for me, intimacy is a important part of any relationship I'm in. Physical acts of love are just as important as emotional acts. So it translates further that intimacy in my character's relationships tend to be important, even as their sex drives vary and are radically different.