I believe the greatest benefit coming from same sex marriage, is breaking the thinking about what is family out of the box, and giving it a much need redefinition.
The old family structure, the extended family simply cannot exist in the American culture. There really is a need for social and legal structures to fill the gaps left by the destruction of the extended family.
Social welfare agencies try to fill that gap, but they only address the extreme cases and they haven't really figured out how to do it efficiently yet.
This bill would push that envelope further, and I hope we see some creative redefinition of human relationships that will work better than the old stuff, which is just not working in today's culture.