In Christian philosophy, many ancient philosophers such as Aquinas and Augustine speak about the "good of marriage." Marriage is "good", they argue, because it leads to offspring, chastity and permanence. See here for a lengthy article on the topic.
What is the "good of marriage" in Jewish thought?
Perhaps according to the Rosh, who doesn't view kiddushin as a Mitzvah, marriage has no inherent "good." The "good," rather, is external, since kiddushin is just one way to lead to the goal of having children. But, according to Rambam, who views kiddushin as an independent Mitzvah, what "good" does he believe exists in it?