When running DirSync:
New user, group, and contact objects in on-premises Active Directory are added to Office365; however, Office365 licenses are not automatically assigned to these objects.
Attributes of existing user, group, or contact objects that are modified in on-premises Active Directory are modified in Office 365; however, not all on-premises Active Directory attributes are synchronized to Office365.
Existing user, group, and contact objects that are deleted from on-premises Active Directory are deleted from Office365.
Existing user objects that are disabled onpremises are disabled in Office365; however, licenses are not automatically unassigned.