To me, I consider poly to be something of a sexual orientation, less of a lifestyle per se.
That is, even when I'm in a single loving relationship, the intimate connections, the desire for other forms of connection, all of that stuff is still there.
For ME, the difference between mono and poly IN MY CASE would be denying myself the ability to "be me".
I'm not one of those militant poly folk. I describe my own feelings on poly as an orientation, and I give equal credit to folks who would say the same about being mono.
Other than that, I don't think there are benefits to mono vs poly, honestly.
I will say that I think people who identify as poly GENERALLY are better at relationships IN GENERAL. This doesn't mean that people who are poly ARE better naturally. The world assume's you're monogamous and it takes courageous, strong and adept people to stand up to the world and say "I defy your assumption". People who aren't great at relationships generally don't build that strength, and especially enough to maintain multiple ones at the same time.
A strong relationship will be wonderful and joyous, difficult and nervewracking. It doesn't matter if it's mono or poly and both can be fulfilling IF it suits your nature. The only benefit or drawback to either or both would be "it is natural to me".
Connection is the path to passion. Passion is not the path to connection.