The ability to view trading inventory prior to depositing your points/weeks, or paying a trading fee.
Confirm-First refers to a type of booking a timeshare trade. You view available inventory without needing to first deposit your points, allowing you the ability to ensure availability before committing to an exchange. Not all vacation clubs have this arrangement with the exchange company they are affiliated with, so it is a worthwhile feature to consider when purchasing your ownership initially.
You can still get on waitlists, or open an ongoing search for your requested dates or locations. Keep in mind, you will be required to pay a trading fee if you want to keep a search open, but will not have to deposit points until the reservation is confirmed.