What is the difference between field mappings and the data wizard?

Both features can send data from Salesforce to Mailchimp. 

The data wizard has many advantages over the Salesforce to Mailchimp field mappings:

1. It both creates and updates Mailchimp members, each wizard using its own mappings.
2. It works with any Salesforce object or email field.
3. It is run by a single user on a schedule.
4. It runs as scheduled Apex, which is efficient and less likely to conflict with other automation or apps.

Field mappings don't subscribe Mailchimp members on their own, Instead, they are only used when:

1. You add a person to an audience via our contact or lead component. 
2. You edit a Salesforce contact or lead that is already on an audience. Changes to mapped fields will be instantly updated in Mailchimp.
3. You are subscribing a member via an invocable action.

Note: Since Field Mappings use triggers, any user who might do one of the above must have one of our permission sets. Your custom automation or validation may also conflict with our trigger.

Field mappings also sync in the Mailchimp to Salesforce direction. These mappings are used only during the primary sync. See Field Mappings for more information.