Unallocating bookings makes it easier to move bookings around the calendar. It is useful to maximise occupancy, as you would be able to fill unnecessary empty spots in the calendar.

To unallocate a booking, simply click on the "Unallocate Booking" button in the booking page of a booking. 

Confirm with"OK" and the system will show the unallocated booking above the calendar:

From here, you can re-allocate the booking to a different room if you wish.