Obviously a prenuptial agreement only becomes relevant at the point where you are getting married, and so won't be relevant at the point where you meet or even for the initial phases of the relationship. For me it really comes down to the specific situation. It's not one I've had to deal with because my wife and I have built our wealth and assets together. We had a conversation recently about how we view the money that we each individually have in our accounts (most of our bank accounts aren't shared, so things like savings are generally in the possession of one or the other of us), and she pointed to certain accounts and money that she has that she does consider to be hers and not ours. And that's fine, because even though I don't feel the same, we ultimately use our money generally for the benefit of the family as a whole, so we end up at the same place. And if we were to divorce, in principle we'd start from the position that everything is shared.
There are clearly situations where people may feel differently, and I think that if you've accumulated a significant asset (such as equity in a house) before getting married, it's understandable that you might want that to be ring fenced in the event of divorce. But then, you could also argue that unless and until you're ready to have all of your assets shared with your other half, you shouldn't be getting married at all. There are a lot of variables, such as the other assets in the relationship, the respective value of those assets, and so on. There are also practical considerations. If, for example, you would be living in the house that your other half owned, the more you contribute to the upkeep of that house (including mortgage payments as well as other work) the more claim I think you have to owning part of it in the case of a divorce (and the law takes a similar view). So it really does depend. If my other half wanted to sign a prenup it would very much depend on why and how reasonable I thought that was, though it's an issue that should be well apparent long before you get married. If he demands it and you don't want to then it may be a dealbreaker, but I'd hope in most situations with established relationships that there would be some compromise to be had.