Before enabling this Workflow, you must enable first enable the State and Country/Territory Picklists in Setup. Steps to validate if this is set up you can review the setup items here.
If you are using custom "State and Country/Territory Picklists" in your Salesforce environment, with this workflow, you can check if your Account Records have:
A valid Billing State Code under the Country Code of "US"
A valid Billing State Code under the Continental US 50 States
Once you deploy this workflow, you can use these two formulas as a gut check to validate that your Accounts are in line within the US Country Code as well as US State Code.
