If you have accumulated some assets, and you care who will receive those assets after you die, it’s time to write a will.
Anyone with minor children definitely should have a will. In it, you can name the person you want to raise your children, should something happen to you and your spouse. Discuss this carefully with the prospective guardian, to be sure he or she is up to the job. Also, name an alternate guardian in your will as a backup.
On the other hand, if you’re a young adult, have no children, and own few possessions, you probably don’t need a will yet. The state would distribute your possessions to your parents. But if you’d rather leave your car to your girlfriend, or your prized Spider Man comic book collection to a favorite nephew, then a simple will is a good idea.