I've had 3 and 4-ways, but they were always with my partner and they were always all about sharing the experience with my partner. We always did it together, and neither of us had any interest in doing anything without the other. The other parties were just there basically as sex toys. In fact the only piece of advice I ever give people about 3-ways is to always do everything together as a couple.
Having a 3-way is absolutely not the same as being in an "open marriage". Most people I know looking to have a 3-way are looking for a new sexual experience with their partner. So far every single account of an open marriage I've ever heard/read had nothing to do with "sharing" and was always just some elaborate excuse to fuck people outside of the relationship.
Cheating is any activity not mutually agreed upon as acceptable within the relationship. Any promiscuity that isn't covered up in lies and deceit, that is honest and practiced within mutually chosen parameters is simply non-monogamy. There is a difference. You turn up your nose at the idea of someone in a non-monogamous pair being truly committed to each other. I turn up my nose at the idea of treating sexual partners as objects. Grosses me right the fuck out. Therefore, I would never operate that way, but I'm glad it's an option that works for some people.
When I was the regular third with a couple, they treated me like a human being to whom they were mutually attracted. We had long conversations, went out together, and were friends. I wouldn't have had sex with them otherwise.
When I could no longer tolerate the nature of the sexual aspect of my marriage, and I had exhausted all other ideas for improving that connection, I suggested that we put monogamy aside. I wanted my husband to make up for not having really dated as a young adult so he could learn about himself what I'd learned about myself in my late teens and early 20's. I wanted to be reminded of what I'd forgotten in our basically sexless relationship, and see what else I could discover. For us, it was about going out into the world and seeing what we could bring back from it to benefit our love.
At first I met with individuals. Then, one of those individuals became my primary sexual partner and we would swing together. (Meanwhile, my husband neither took new partners, which I now know was out of fear of exploring same-sex relations and a lack of interest in sex with women, nor did he try to improve sex with me. He continued to lack spontaneity and continued to reject most of my overtures while making none of his own, which is how an extramarital partner became my primary sexual partner, with my husband's consent. The rule was to come home and be clean and in bed before my husband awoke so he'd know I was safe and could snuggle before work. That partner and my husband became friends, and though he and I both tried to set my husband up with suitable partners, all were rejected for flimsy reasons.)
In talking to other swingers, it was usually very much the same story. Whether they played together or apart, they played to have something new to bring back to each other. You do not know what you're talking about because this is just beyond your understanding at this time. Maybe someday through experience or reading I'll understand the appeal in having sex that is purely impersonal and objectifying, and you'll understand how some people can benefit from non-monogamous sex lives while being completely committed to the health and growth of the relationship at home. Or not. Understanding is not required to coexist. However, coexistence does imply a lack of harsh judgement.