Here is a good article from RocketLawyer on why you should have a Last Will and Testament.
5 Reasons You Should Create a Last Will
1- To appoint a guardian for your children
No one knows their children better than a parent and, if you pass away without a Last Will and Testament, the State will decide who should care for them. You can choose a guardian for your children in your Will and make sure they’re looked after by someone you love and trust.
2- To protect your business
Making a Last Will and Testament (and using Living Trusts) is a good way to pass your company to your heirs or the co-owners of your business. A full 70% of family owned businesses do not last past the first generation and the main reason for this is lack of estate planning.
3- To decide who receives your assets
Whether it’s a family heirloom, a classic Corvette, or your savings, you should decide who receives your belongings after you die, not generic state rules. These rules might not meet your wishes and never include provisions for those not related to you, like close friends or mentors. Make sure your loved ones get the assets you want them to receive.
4- To provide for a favorite charity
Wills don’t have to be just for friends, family, and loved ones. They can also be used for altruism. Including a charity in your Will is a great way to give back and make sure your assets are used for a good cause.
5- To make a difficult time less difficult
Losing someone is incredibly hard, and the last thing any of us want to do is spend those hard times haggling with lawyers and family members. Making a Will keeps your loved ones from having to deal with bureaucracy in a time of sadness.