In addition to all the practical reasons anyone has for making a will, as a writer you need to be concerned about what is going to happen to the copyrights in your works. They could be your most valuable assets. Because any copyrights you hold will last for your lifetime, plus 50 years (if copyrighted since January 1, 1978), a copyright is something you can leave to your heirs in your will, and they can collect royalties or reprint fees long after you are gone.
Since there are any number of ways to divide these rights, you will want to think about it and make your wished known in your will. Since a copyright embodies a number of different rights, you can transfer them in their entirety or divide them between a number of different heirs as multiple shares. For example, a novelist might leave the dramatic rights to one heir and the translation rights to another. You could give the rights for the whole 50 years (after your death) to one person, or it could be divided, giving the first 25 years to one and the second 25 years to another. You actually can do it any way you want as long as there are clear guidelines to be followed. When you are having a lawyer prepare your will, be sure to let them know you want to make provisions for your copyrights and supply all the information needed to do so. Any such choices you fail to make now, the state will make for you later.