It lends to loyalty between the couple if they do so, especially if they hold off on sex altogether until marriage. The huge downside, however, is that you've already made the biggest commitment you can make before you've brought yourselves to the higher emotional level sex brings. What if you find that there's a big sexual funk between you? Would that effect the marriage? Is that something you might have wanted to know before you made such a big decision? Altogether, waiting is a very bad idea. You may have more loyalty, but it might be loyalty to something that wasn't everything you hoped it would be. This is primarily a religious idea. Loyal couples who go to church and make babies keep the membership numbers up.