This setting works in both directions, depending on which way products are synced:
Products sent to Magento – decides whether products that already exist in Magento are updated.
Products sent from Magento – decides whether products that have been updated in Magento are picked up and sent.
Yes – existing products are updated / updated products are loaded.
No – existing products are left as they are / updated products are not loaded.
Good to know
This setting is required.
When updating products in Magento, choose which fields to update in Fields to update.