If one or both have assets, then a pre-nup is a great idea.
Many people feel that it is a bad way to start a marriage, because of the idea that you are planning for a divorce before you even get married and many feel that it is a trust issue, but a pre-nup is about individual security and also about ensuring that your own children will not lose out in the divorce. If you have a lot of assets to your name going into a marriage, you have children and the marriage collapses and you end up getting divorced and you lose everything in the settlement, then your own children lose out in the long run and you may find yourself not being able to financially provide for your children because you have lost so much. I often tell people who get upset at the thought of a pre-nup that they wouldn't drive a new car out of the lot without insurance, because no one would imagine that you'd buy a car to crash it, but accidents can happen and it is always best to insure it, just in case.
It's nasty business, but there is nothing wrong with insuring your personal financial security.