In swinging circles there is a concept known as "taking one for the team."
By my own definition, it's when you agree to "play" (have sex with) with someone you're not attracted to so that your swinging partner can have access to someone they are attracted to.
Have I done this before?
Yes, I have. Did my partner ever do it for me? Yes, he did.
It's sort of a fine line. I mean, how "into" someone do you have to be to decide to "play" with them? That's a question that everyone has to answer for him or herself. And how your partner's interest in the other half of the couple factors in to your own interest definitely makes for compelling situations. (I prefer the more positively-charged word "compelling" to "drama." See this post for more on the D word.)
There are a lot of swingers who emphatically proclaim "I never take one for the team!"
And that's fine; the whole lifestyle is about personal preferences. However, any couple that goes into swinging thinking that every time they play with another couple that there's going to be equal attraction and chemistry between all parties involved is fooling themselves.
There are going to be times that you feel like you're getting the better end of the deal and other times where you feel your partner is. It's exceedingly difficult to find two couples where everything is equal and balanced. And there are factors besides attraction. What about stamina? What if the male half of one couple finishes very early whereas the other takes a very long time (I have had this happen quite a bit actually and been on both sides of it). It can throw off the timing of the whole session. One couple may be lying there twiddling their thumbs while the other is still going to town. Throw other preferences in like foreplay, toys, and bi play plus performance issues and there's all sorts of opportunities for things to go awry.
I think that's why it's best to go into everything with an open mind and relatively low expectations. I try to have the attitude that I'm there to have fun, whether that's sharing a laugh with new friends or a mind blowing orgasm. Either way, I come out on top. Add my partner having a good time and then no one is really "taking one for the team."