For me, it's mainly a religious thing, but I agree with it. Sex is a sacred, and wondrous thing, and should be saved for that one person that you want to spend the rest of your life with; the one who you want to give everything to. I also think of it like a savings account. By waiting until marriage, you're saving up that currency, rather than spending it all the time, and never giving it the chance to grow, you're taking care of it and nurturing it. And by the time you get married, you've saved up so much, that the payoff for cashing it in will be well worth it.