What happens when I uncheck the Update My Leads and Contacts option when I launch my email campaign?

When this option is checked, VerticalResponse will update the VR Email History and either the Activity History or Campaign History objects (depending on the type of list) with an initial indication of Sent for all Leads and Contacts mailed to. If you uncheck this option prior to launching your email, this data will not update in Salesforce for Leads and Contacts in your list.