A will protects your interests after you are gone.  If you want to make sure a certain person gets a special item, leave money to a favorite charity, or you want to have your close friend instead of a relative to receive most of your money or property, make a will.
If you do not have a will, state law will determine where your things go.  A will can prevent family and others from fighting about your property in court.
https://estate.findlaw.com/wills/top-ten-reasons-to-have-a-will.html