Your users that have Salesforce Platform licenses will require this configuration at least at the Profile level. If this Custom Setting is not configured, the Opportunity field is copied to the Adobe Agreement and prevents Platform License users from sending agreement documents for eSignature and results in the following error:
"You do not have the level of access necessary to perform the operation you requested. Please contact the owner of the record or your administrator if access is necessary. (echosign_dev1__SIGN_Agreement__c)"