I don't know whether I am the right person to answer this question because my stories are entirely self driven, in the sense that they drive me. The idea comes to me and I sit and write it, the words and characters going in their own directions. Sometimes that direction takes them into sex, sometimes not. I don't use sex as a device or a hook and neither do I balk from doing it if it comes to me.
I absolutely agree that in oder to mantain writing integrity, which is important to me, a writer should follow their heart and their art. They either listen to their muse or they don't in which case the muse gets pissed and either leaves them or messes with them.
The question should be self answering... if the story asks for it then do it, if it doesn't don't. If you put in sex just for the sake of it, if you don't really want to do it then the scene is simply not going to be good. It will be wooden, contrived and boring. There has to be feeling in it to get feelings out of it.