Most people think of their will as the document that controls who gets their stuff. For many retirees, the will controls less than 30% of their estate. The rest passes via beneficiary designations — and those designations OVERRIDE the will.
Accounts that pass via beneficiary designation (NOT through will): 401(k), 403(b), IRA, Roth IRA, life insurance, annuities, pension survivor benefits, bank/brokerage accounts with TOD (Transfer on Death) or POD (Payable on Death), HSA accounts, 529 college savings.
Accounts that pass through will: anything in your name without a beneficiary designation. House (unless held in trust or with TOD deed), personal property, individually-owned brokerage without TOD.
For a typical retiree with $1M in retirement accounts, $200K in brokerage TOD, $250K in life insurance, plus a $400K house — the will controls the house and personal property (~$450K), while beneficiary designations control the rest ($1.45M). Updating beneficiaries is 76% of the estate's distribution.