I found this decent little tidbit on r/sex the other day on good and bad reasons to open a relationship. I'd like to add the single poly perspective and say that you can also define yourself as poly if it's something that makes you happy. Even if you're not in a "relationship" yet and you just want to be open and honest with anybody you might wind up dating that you won't be entirely exclusive. I understand that relationships are work, and that you can't be happy 100% of the time. And you don't have to reach bouncing off the walls types of happiness. That shit can be irritating.
Just...general okayness with open/poly/whatever being what you want and who you are.
Also, there's this pretty neat article up on Vice about poly. The closed vs. open relationship chart near the end is something I haven't seen before, and interesting.