As an introduction it is a means to something more intimate.
In addition to really enjoying the feel of a healthy cock in my hand, it is definitely therapeutic. I injured my elbow late in the summer, and my doctor told me that I should do mild flexing as often as I could. So - my lucky boyfriend offered himself as my therapy aid - I get to flex my elbow with him all the time. We made it into our therapy game - medically necessary, of course.