How to Read the Result
The figure is what one closed ticket costs your desk to produce. Compare it with what a client's plan pays you per ticket at their usual volume: if the plan pays less, that client costs you money every month they are busy.
When Not to Use It
Do not use it for project work or on-site visits, which are priced by the hour and carry travel. And do not use a month when the desk was short-staffed or buried in one incident, because the number describes that month rather than your business.