In basic, the property of individuals who pass away without a will is dispersed according to basic rules of succession that have been in place around the world for centuries by means of a decision of next of kin.
State laws that govern intestacy are designed to approximate what most people would state if they were to make out a will, keeping the interests of specific recipients in mind, and this would especially use to reliant children. The lives of most individuals aren’t that easy, and when you draw combined families, non-familial relationships and same sex couples into the equation, the laws of succession are most likely not going to be consistent with your wishes.
Aside from financial matters, if you pass away without a will specify laws will decide who makes medical choices in your behalf should you become incapacitated. Even if you have no financial possessions to speak of, you have to think about whether or not you desire state laws to decide these things for you.
In a nutshell, if you pass away without a will, the state will make all of your decisions for you.