The "Review Bookings" panel is where you can see all of the information that Visitors submitted when they booked an Event on your Calendar. You can also see what Event that person has booked, the time they booked it, and their current booking status (Pending, Accepted, Rejected, etc.). If you have bookings that you no longer want to keep this is where you can delete bookings as well. See the image below:

By default when you delete bookings they will no longer show on your "Review Bookings" panel. If you want to see your deleted bookings you'll need to click on the blue "Show Deleted Bookings" button towards the top of your screen. See the image below:

If you want to hide your deleted bookings again all you need to do is click on the blue "Hide deleted bookings" link towards the top of your screen where the "Show deleted bookings" link used to be.