When you are troubleshooting domain controller replication issues, nobody wants to wait until the DCs decide to replicate on their own. Or, when you are putting a new GPO and it is the middle of the night and you just want to see if the thing worked now so you can go to bed. In my experience, this same command works with all version of Windows Server and all functional levels of active directory, so enjoy!
From command line (as administrator):
repadmin /syncall /AePdq