Database synchronization brings the database in line with the domain model. You do not have to manage your database; you simply edit the domain model and the rest happens automagically.
In version 3 the synchronization algorithm has been rewritten and it can handle more cases than before. To do this it keeps an administration in special system tables. Because of this you should not edit the database yourself: do not delete or rename columns or tables. Otherwise, the administration will not reflect the real database structure and synchronization will likely fail.
It should not be necessary to modify the database yourself, so whenever you feel the need to do so, let us know through the forum or the support portal and help us improve the automatic synchronization of databases.