What is the difference between insert/update and update/insert in the target table in owb?

What is the difference between insert/update and update/insert in the target table in owb?

Insert/update: The insert operation is performed on any introduced rows first. If the insert operation fails, the update operation is executed. If no matching row is used for update, insert is executed.
If insert/update is selected and the default processing mode is Row-based, you must set a unique constraint on the target.
If insert/update is selected and the default processing mode is set-based, owb will produce merge statements in the database.

Update/insert: To update any introduced rows, perform the update operation first. If update/insert is selected and the default operation mode for the target is set-based, owb will generate the merge statement in the database.