The benefit to marriage is that it's about committment before and through God. It's not bulletproof, but that's not the idea. The idea is that it's a relationship based on mutual respect and selfless love that includes intimacy, rather than just bare intimacy with no thought to latter repercussions...
Case in point: suppose we take the difference between a person who sleeps around without any self control, and a man such as my father who only sees my mother. The former situation is unstable and often causes dysfunctional results (STDs, unplanned pregnancy/parenthood, psychological illness, heartbreaks, etc.). The latter situation is stable and beneficial on all levels, however.