What is the difference between a snapshot report and a snapshot difference report?

A Snapshot report allows you to download a report which provides full details of the version of the Dow Jones record as it was when the potential match was created with your customer 
record.

A Snapshot Difference report  allows you to download a report which details the differences between the profile of the Dow Jones record when the potential match was created and the current profile of the Dow Jones record (i.e. the record that has been updated by Dow Jones, which has triggered a 'notify change' event).