If you die without a last will, it's called dying intestate. There would be no information about how you wanted to distribute your assets. Even if you think your family would know your wishes, they might not uphold them in court.
The probate process, in which the court decides how your assets would be distributed, follows. The court follows the intestacy rules that might not be what you want.
Also, the probate process can take anywhere from three months to years. During this time, your assets would be frozen.