A Will is a legal document that names guardians for your minor children and/or determines who will receive certain property or assets when you pass away. Without a Will, state law decides who gets what, without regard to your wishes or your heirs' needs.
In addition, without a Will naming a preferred guardian, the court will not have any guidance as to who you wish to be appointed as guardian of your children. If there is no Will, state courts try to do what's best for minor children and usually appoint a close relative as guardian (if one is available). But, if there is a Will, the court will generally give preference to your named guardians.
If you don't have minor children and intend to “fully fund” your Trust (meaning transfer 100% of your probate assets into the Trust before you pass away), a Will may not be necessary. However, it's actually pretty hard to make sure that everything you own is put into your Trust before you die, so a pour-over Will, transferring anything you forgot into your Trust, is an important backup.
If you don't think a Will is necessary at this point in your life, read our blog post on why that might not be the case. We also have some suggestions on how to get started, if like all of us you've been too busy to begin the process.