The addition of service applications has produced many benefits to Microsoft SharePoint 2010, but it has also created some challenges. The major benefit is that one farm can consume (use) another farm’s User Profile Service (UPS). This keeps all the user profile information synchronized without the need for replication. Replication is still a valid option for keeping user profile data in synchronized among various farms. The difference is in control. If you want centralized control of all the user data, then consuming the UPS is the proper method to choose.