I have always not understood this report for this reason:
The change in bookings is supposedly listing any price changes in a previously written sales order, but the subtotal for the line is always positive even though the total for the sales order has been reduced.  
For instance, we booked an order on 4/11 for 2each of 2 items, the total for the SO was 18600.  A week later, the order was reduced by 1 each for a new total of 9300.  
The booking report for that week lists the SO under change in Bookings with a positive change of 5200(?) which has been added into the total bookings for the week, not subtracted.