There are probably more misconceptions about polyamory than any other lifestyle choice. The poly community likes to discuss them at length, and bemoan their prevalence in society at large. (If you're unfamiliar with polyamory, Franklin Veaux's More Than Two is a good resource for explanations and insights.)
Some of the most common misconceptions include the idea that jealousy is rampant in poly relationships, that poly people are unable to commit, and that polyfamily homes are bad for children. These are all important issues and, yes, very common ideas we have to combat.
However, I've noticed a fundamental misconception about polyamory that nobody seems to be talking about, one that is often even touted as a reason to consider polyamory in the first place: that polyamory implies a constant "new lover" sort of phenomenon. This idea even touted as one of the benefits of polyamory. The fact that you have new lovers keeps things exciting and interesting.
The simple truth is that most of us don't have a constant stream of new partners. A common poly mantra is "infinite love, limited time." There are only twenty-four hours in a day and seven days in a week. Even if I knew a dozen wonderful, brilliant, amazing people, I couldn't date all of them. I don't have that much room in my life.
At its most basic level, the thing that separates polyamory from swinging or the casual dating many monogamous people engage in is commitment. Poly people are not just having sex with more than one person, they're loving more than one person, and that sort of relationship takes time to build and maintain.
I currently have two partners. I spend three days a week with each of them, and the seventh day is mine to do with as I please (I often spend it with friends I am not dating). Even with all the time we get together, my partners and I all feel like we need more. More time. More opportunities. More events. More relaxing. Just more in general. We all wish we could add hours to every day and days to every week, and we all know we'd fill them with each other and still want more.
I wish I had time for other partners, because there are people I'd love to spend more time with. I know many awesome people I'd like to date. Some of them might even like to date me. But right now I can't possibly make time to cultivate those relationships.
Poly people often call this being "polysaturated." Yes, we do love our puns. But polysaturation is a common trend in the poly community.
So I have no more ability to take on new partners than someone in a monogamous relationship, yet I am far more satisfied in my multiple relationships than I ever was when I was monogamous. How can that be, since all the hype is about having new lovers?
For me, the major benefits of being poly have nothing to do with taking on new partners. My boyfriends are wonderful complements to each other. Ryder is loud, energetic, outdoorsy, and intense. Rusty is quiet, calm, nerdy, and easygoing. I get very different things from each of them, most of which couldn't be supplied by the other.
I also feel extremely loved, in ways I never felt when dating one person at a time. Both of my relationships are still relatively new, and both are still in the giddy NRE stage. This means that I am overwhelmed by feelings of love. Not only do I feel incredibly loved by my partners, but also by my metamours (my partners' other partners), and by the rest of my pod in general. Because so many people are so intimately linked, we create a family.
I also wonder if variety is as good as novelty when it comes to excitement and arousal. Monogamous relationships often get "comfortable," meaning you stop being excited by your lover. Frequently, the introduction of new lovers into comfortable monogamous relationships reinvigorates the old pair, giving new excitement to their time together. It's hard for me to judge the degree this comfort happens in poly relationships, since, as I said, both of mine are still new, but I think it's possible that simply having more than one partner is enough to keep things exciting and interesting long after the NRE wears off.
Finally, limiting yourself to your current partners while in poly relationships is your choice. In monogamous relationships, you may desperately want to be with someone else and only hold yourself back out of a sense of obligation to your partner, or from the fear of losing them (or, commonly, you don't hold yourself back and just hide this fact from your partner). In poly relationships, limiting your number of partners is a choice you make for yourself, so you don't end up resenting your partners for it.