If your nephew had millions (literally) he wanted to protect, in the event that the marriage would end in divorce - a prenup may be a good idea. Think of child-stars, or pop-stars who marry people who aren’t rich. People with millions of dollars that they had going into the marriage.
But, if he is like 99% of the rest of America - all it is going to do is alienate his bride.
If he is like 99% of America, there is a 50/50 chance he will get divorced, and 3/4 of the time, the woman files.
but lets be charitable and say 33% of first marriages fail.
If you were going to walk into a door, and you knew there was a 1 in 3 chance you would be shot in the chest, would you want a bulletproof vest?