The Huffington Post has an article on the reasons that some same-sex couples adopt a name change. This can be done to create a sense of relation to your partner that is both practical and personal:
Andy Page, who grew up near Birmingham and hopes to someday adopt a child with his husband Lee Hawk, a gay couple cannot adopt jointly, so they must choose one person to be the adoptive parent. “In our case, Lee would be the one to adopt. He has a great job, insurance, a pension. I would take Lee’s name of course. It would just be easier for the child for us to all have the same last name.”
“Lee is my whole,” adds Andy. “Taking his last name would be a cool way to be a little part of who he is, to show my commitment to him, and I like that.”
Same-sex couples may also feel that having a shared name gives their marriage more authority, says MaCabe, the family law attorney. “People also do it for a need of acceptance in a larger world where there is one idea of what family looks like and to fit into that box.” But as the idea of what family looks like continues to evolve, with each state free to define it differently, the process of changing names can be complex and expensive.