The Available Nights report shows the number of missed nights during a date range. It includes a "# of Nights" columns so that you can instantly see where the big gaps are across properties and date ranges. If you export this report to Excel, this will help you not have to create a formula for that as well.
The grouping will show you the total missed nights per property or owner, so that you can quickly see which property or owner is having difficulty with occupancy.