DirSync - "Update Last Pushed USN" feature explained (4379402)

What is the new "Update Last Pushed USN" feature in the Directory Sync local Environment settings and when should this setting be used?

If you select a local Environment in ODM DirSync and click Settings | Domain Controllers you will see a "Update Last Pushed USN" checkbox. Here is how this new option should be used:

Why would I want to use this feature? This feature may be useful in a situation where you want to re-read objects from the Environment, even though they haven't changed, but you don't want to perform a full read of the entire environment. In a very large Environment, a full read could potentially take several days. Using the "Update Last Pushed USN" will allow you to sync objects that haven't changed without performing a full sync.

How would I use this feature? Here is an example use case:

1.) The following user has been identified as not being synced to the target when a workflow is ran. Additionally, when going to the source Environment | Details, this user is not found in the list of Users:

(Screenshot above from the source Active Directory Users and Computers)

2.) For this example, we will now go to ODM Directory Sync and set the "Last Pushed USN" value below the value of the missing user object:

3.) From the screenshot in step 1 above, we know that the Last Pushed USN will need to be set to a value below the value in the missing user object (147601). Since there may be other affected users in the same USN range, it may be best to set the Last Pushed USN to 100 or 1000 below that of the known missing user: 

4.) We can now uncheck the "Update Last Pushed USN" checkbox to commit the change and protect this value from accidental updates:

5.) Run the workflow, which will now read all objects greater than or equal to the Last Pushed USN value you just set.