Open Marriage

Jessa • Unofficial nomad. Aspiring midwife. Fierce lover of naps.
I have always been taught that marriage is based on mutual trust and exclusiveness. It's been engrained into me that if one or both of the spouses has been with lots of other people, it's hard on the marriage because then there's nothing special and unique to their own relationship. This is why Christians tend to teach abstinence.
I am very well aware at this point that there are other ways of going about marriage than the traditional Christian/exclusive marriage. But how do they work? If you're in an open marriage (or any other kind of marriage), why does it appeal to you?
To be clear, I'm absolutely not shaming anyone. I'm curious!