Few Employers have multiple companies but Centralized DHS Setup allow employers use only one central company to E-Verify all the candidate being hired across all companies.
Look at it more like a Parent-Child relationship.  
This Parent Company has the This central company hold E-Verify Web Services account and MoU with Ewith E-Verify certifying the use of this company as a master (Parent) for E-Verification across other companies (child). Which means only one Program Administration Account and only one Web Services Account.
This Central E-Verify situation is like a 1:many mapping situations.
Now We currently have to have a 1:1 mapping for each company value and Webservices account in our system. . 

Who can access the Centralized DHS Setup?

The System Administrator is the only user who can access the Centralized DHS Setup.

How to change the product setup for Centralized DHS option?

Click the Menu icon and select Product Preferences under Product Setup.

If the product is Smart Onboarding click Details under Onboarding Default Option. If it is only E-Verify Product click Details under Smart I-9 E-Verify. 

Let us first consider changing Product Preferences for Smart Onboarding product.

The system is delivered with Centralized E-Verify property disabled (set as No).

Set Centralized E-Verify Property to Yes and click OK.

For changing product Preferences for E-Verify product, click Details under Smart I-9 E-Verify.

You will notice the Centralized E-Verify property default value as "No".

To enable the Centralized DHS, set the property value to "Yes" and click OK.

Save the changes made to Product Setup.

How to access Centralized DHS Setup?