Sync Services is a central database on your Macintosh computer that keeps track of applications and devices that share information. You can use Sync Services to synchronize your Outlook contacts with other applications, such as the Apple Address Book and MobileMe.
If you have an Exchange account, you do not use the Sync Services central database. You are syncing to the data on the Exchange server. For this reason, you’ll have fewer issues with sync . . .
Continue Reading: Sync FAQs