You don’t, unless you care about where your property goes if you die. Oh, and, if you have a minor child, you may want to give the court some direction on who should raise your minor child.
It is axiomatic in U.S. law that one may dispose of his or her property according to his or her own wishes. People usually come in to write wills that split property evenly among their children. But that isn’t what they have to do.
Married couples usually write what we call “kiss me” wills: you get everything if I die, I get everything if you die. But what happens if you die together?
If you have a minor child and want a will, figure out who would be best to care for that child and ask them before you put it in your will.
One important decision is who would execute your will. A good executor (or personal representative) will make a considerable difference. In Iowa, the executor should be an Iowan.
See a lawyer to make sure your will is written properly according to the law of your state.