I have never requested it, but occasionally done it when the woman I had arranged to meet wanted to have someone else be there.
Most often, I was a training g example for the new girl. She either watched in one case, or participated with coaching from the more experienced one. One time it was a regular of mine who brought her real world SO. My regular was very bi, and her SO was straight gay, who expressed she wanted to try a cock. My regular offered up mine, since she felt I was no threat to steal her GF. That session went an hour, then we went out to dinner, then the rest of the night at my place. That was the only experience I would try to duplicate because it was a great time over and above the sex (which was very good as well). Other than that one, some were interesting because they were different, but I agree, over rated. I find four things is the most I can focus on at one time, and every woman I know has a mouth, two nipples, and a pussy, so that is four and keeps me occupied.