Some people call it spiritual growth, or the path of the Bodhitsatva, but I prefer my Buddie Evan's definition: "...becoming more awesome". I think that life is pretty awesome and I like who I am but I also believe that I have room to become more awesome. The practice of having multiple intimate partners helps me to become more awesome.
Love causes humans to become more awesome. It has been my experience that the more I open up to love the more awesome I become (and feel). To have more than one person within intimate loving space gives me energy and inspiration to become a better person (and it feels really good).
Love can be compared to the light of the sun that shines and causes all the shadows and demons to come out to receive the healing light of love. Love causes shit to come up. Lots of love causes lots of shadows to be unearthed. Fears, insecurities, selfish desires, social blind spots, tensions, doubts, all of these come up.
Poly is incredibly effective here because it makes it easier to identify my shit as my shit. When I have the same insecurity or fear come up with multiple people, it is clear that it is my place to grow rather than simply my lover being inconsiderate neurotic. Then, when the growing edge is identified, I have multiple perspectives and supports to help me understand and work through the difficulty.
You have to be honest with yourself as well as others. It is sometimes hard to see what you really want or what you are really comfortable with. For whatever reason, when there are multiple people this becomes more imperative and it becomes harder to hide or shirk responsibility.
You have to learn to communicate. I heard an acquaintance comment that "...Polyamory sounds like fun but it requires too much communication for me." This young lady obviously knew her boundaries and what she wanted to take on. In contrast, the communication requirements are what turn me on! It is one of the tragedies of life that we are unable to effectively communicate our feelings and thoughts to another, that we fail to see eye to eye with our loved ones. Anything that can increase my ability at doing so is awesome in my book.
Being Poly helps me to be a better lover. Different people like different things. Playing with many people I can explore what works for one and another. Sometimes I learn something from one that works with the other as well. Also, if I am not getting my needs met with one of my partners, I can usually get it met with another. It does not need to become a point of contention in our relationship. I can let her engage with me the way she is comfortable and do the uncomfortable exploration with my other partner.
There are many more reasons but this is a start for now.
