How does merging a record affect Campaign Monitor data?

Merging Salesforce contacts or leads can have different outcomes depending on the scenario. It is important to note that when a merge occurs in Salesforce, the losing record(s) will be deleted. So it's the same as if you had independently deleted a record in Salesforce. You may also have other processes or triggers on the contact or lead objects which can again cause problems. To help we have put some common scenarios and outcomes together here.