A prenuptial agreement could be hard to discuss with your significant other, but it's best if you talk about it well before you get married. Once you're married, you'll have to sign a post-nuptial agreement and it may be too late to agree on one.
A prenuptial agreement is good for a few reasons. First, it helps you protect yourself. Second, it can help your future spouse protect themselves. Third, you can both see if you're willing to work together to protect each other in the future in the case of a divorce.
Of course, there are some things a prenuptial agreement can't do. It's not able to determine future custody arrangements for children. It's not allowed to be extremely unfair (if it is, most courts will throw it out citing the extreme nature of the agreement). Additionally, if you have little time to review it or feel forced to sign an agreement, it could be invalidated at a later date.
What if your spouse wants you to sign a prenup but you don't like the terms?
In this situation, it's a good idea to take the prenuptial agreement to your attorney for a review. Then, you can draw up your own agreement, likely with some changes, that you return to your partner. If they agree, then the more reasonable prenuptial agreement will be signed. If they don't, you can continue to negotiate or refuse to sign the proffered document. Nothing obligates you to sign a prenuptial agreement unless it's going to help you in some way in the future.