Step 12 handled your accounts. This step handles everything else — who gets your other assets, who raises your kids, and who can act for you if you're alive but unable to.
Without a will, state law decides who inherits, through slow, public probate. Without a guardianship designation, a judge decides who raises your children. Without powers of attorney, even your spouse may not be able to pay your bills or talk to your doctor if you're incapacitated.
Typical cost of a complete document package from a reputable online service. It sits here, after the emergency fund, so the cost never competes with your safety net.
Who gets what, and who carries it out (your executor).
Who raises your minor children.
Who makes medical decisions for you, plus your end-of-life wishes.
Who manages your money if you can't. "Durable" means it stays in effect.