When creating a snapshot set, you can choose the backup type depending on how you plan to use the snapshot set, as follows:
Copy backup is generally used for a snapshot set to be maintained on-host and used for quick recovery of a missing or corrupt Exchange database.
This mode creates a snapshot or copy of the transaction log, but does not truncate it. You can choose whether or not to run the Eseutil consistency check.
Full backup is generally used for a snapshot set to be used for snapshot-assisted backup. Full backup runs the Eseutil consistency check and truncates the transaction logs.