For the first 30 days after a VRI week is deposited into the Spacebank, it is available only for exchange with other VRI weeks. The other week must still have the trade power needed to complete the exchange. But if you have a strong enough week, you are only competing with other VRI weeks exchangers for the first 30 days.
If you are own both VRI and non-VRI resorts, the prefrence applies only when you are exchanging using a week from a VRI resort.