
Explanation

Group Writeback is enabled in the Azure AD Connect configuration so groups created in Azure Active Directory will be synchronized to the on-premise Active Directory. A security group created in Azure Active Directory will be synchronized to the on-premise Active Directory as a security group.
Device Writeback is enabled in the Azure AD Connect configuration so computers joined to the Azure Active Directory will be synchronized to the on-premise Active Directory. They will sync to the RegisteredDevices container in the on-premise Active Directory.
Reference:
https://docs.microsoft.com/en-us/azure/active-directory/hybrid/how-to-connect-device-writeback