Synchronizing devices can potentially be an expensive operation. On new installations, where both Smarts Manager and Network Configuration Manager are new to an environment, performance is much better if the discovery of devices is done in at least one of the systems prior to running batch synchronization. Although the active synchronization can synchronize them, it takes longer and is less efficient.
More importantly, keep in mind that some of the functionality in the adapter depends on synchronization. For example, associating notifications with the proper devices and performing credential rolling depends on the internal mapping.
After running batch synchronization, the respective discovery jobs in Network Configuration Manager and Smarts Manager (the pending list) must be executed for the synchronization to complete. Therefore, it takes some time for the synchronization to settle out unless the pending list and jobs are manually executed and run to completion.