If you don't list any primary or contingent beneficiaries
In such a scenario, the benefits are transferred to the policyholder's estate instead, which slows down payouts to the family. The court eventually decides who gets benefits. Those who are not listed on the policy and claim benefits may need to pay estate taxes.
If your beneficiaries predecease you
If you outlive your beneficiaries, it's the same result as if they were never listed on the policy, i.e., no payouts occur. That's why it's important to update the beneficiary list on your policy after a beneficiary dies.