What is a Twin Field?
Salesforce CPQ & Salesforce Billing supports field mapping between certain fields on CPQ and Billing objects. Those fields are called Twin Fields. A mapping is an activity of copying a value from one field to another. That action happens when certain CPQ/Billing automation processes take place. For example: creating an order, creating an invoice, contract renewal or amendment.
Why use Twin fields?
Twin Fields allow to store the important information on core CPQ & Billing objects at every CPQ/Billing process stage. A Quote with Quote Lines represents something that is not yet agreed with the Customer, so it changes to the moment when we have an offer accepted by the customer. We want to store that information when we Order the items from the quote. First, we need it for the reference for the future. Second, when we contract an Order and then amend or renew the Contract, we need information to flow into the Renewal/Amendment Opportunities & Quotes.
Typically you can expect that the bigger CPQ/Billing project is, the more chances of using that feature is.
On which objects the Twin Fields work?
The below diagram shows the mapping direction between Twin Fields on various objects that happen in Salesforce CPQ and Salesforce Billing at certain automation.
And the below diagram shows the Twin Fields mapping in the Salesforce CPQ Configurator
You can read more here: https://help.salesforce.com/articleView?id=cpq_twin_fields.htm&type=5
