The UPSERT operation updates a record if it exists or inserts a new record. This allows you to avoid inserting duplicate data. However, it does not process only new or updated source data, it processes all the records in case if no filters are specified in the task.
As we have mentioned in our previous reply, you can specify filters for data being imported (such as LastModifiedDate > = YESTERDAY) or use state filters (Updated, Inserted) : https://skyvia.com/resources/docs/index.html?importing_recently_added.htm
For example, you can easily create a package, that adds all the new Salesforce leads to Dynamics CRM leads, etc. After this you can schedule it to execute every several minutes, and leads will be automatically added for all the new Salesforce leads, etc.
This functionality allows you to create trigger-action-like integrations or simply load all the new records and updates from one source to another automatically. However, it is not a full-featured replacement for data synchronization, because an Import package cannot perform actions for recently deleted records.
If you encounter any issues with this or have any further questions, feel free to contact us.