A pour-over will is the safety net under a living trust. It says, in essence: anything I still own in my own name at death goes into my trust. Whatever slipped through - the car never retitled, the account opened last year - gets caught and 'poured over' into the trust's instructions.
The honest caveat: assets passing through a pour-over will still go through probate first if they exceed Arizona's small-estate limits. The will is the backstop, not the plan. A well-funded trust leaves the pour-over will with nothing to do - which is exactly the goal.
Every trust-centered plan includes one, because it also does the one job no trust can: nominating guardians for minor children.
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Educational information only, not legal advice. Terms have statutory details beyond these summaries - confirm your situation with a licensed professional.