From: The Shire
I almost feel bad for answering this question because I don't feel that I am the norm or even the majority when it comes to poly people.
Unlike people who consider themselves poly by nature, I'm poly for a specific purpose. Basically, I wouldn't be poly if it weren't for the kink and D/s aspects of my secondary relationship. This means at any given time, my husband and my submissive will always be different types. My relationships are two completely different models. My primary relationship fulfills what I consider my needs and my secondary relationship is pretty much about the aspects that I consider my wants. Should it ever come to pass that I lose my kink or power dynamic interests (it's been known to happen for some people) I'd have no need for a secondary partner.
Right about now is when people start losing their shit because my reasons for being poly don't match up with other people's. To me, being poly isn't about my capacity for romantic love with more than one person, (though it's been known to happen) or any of that stuff that a lot of poly people try to hold over monogamist people's heads because of some kind of enlightenment they think they've found. I happen to be in the section of poly people that look at the realization that says, "hey, maybe it's just not practical to expect one person to fulfill everything that I might want in life". From a certain angle, trying to be somebody's everything has to be a little exhausting.
I haven't been "poly" for a while- but this ^^^^^^ is reallllllly how I see it. When I was in a different situation i chose different people, because I like variety- and they filled different voids because I can't imagine one person being everything for me. Even if my current relationship is mono- I struggle with that sometimes because there are some wants not being filled (and I'm selfish about that stuff).