Match & Update - Don't Add
Salesforce formulas need a setting like RENXT on child objects to allow for control over what happens when a match is or is not found so users can choose not to add new if matches are not found and leave destination as-is if matches are found.
Example1: Salesforce users importing Benevity files link opportunities between employee and employer via a lookup field with the transaction ID. If the employee or employer doesn't give ($0 gift), we're not creating an opportunity. Destination exceptions present because transaction ID is always present and there's no way to make one blank if it's a $0 gift.
Current solution is to create intentional exceptions and process in a separate formula.
Example 2: Client only wants to match to existing campaigns and if incoming value doesn't match, go to exception to catch attention to failed match. If mapped field is Campaign Name and no other field is required, OC will create new campaign.
Current solution is to make another field on the object required or create validation rule in SoR to reject.