OU assigned to exp orgs

Expenditure orgs under the Project Expenditure/Event Owning Organization classificiation have fields to assign an Operating Unit and a Calendar.  I understand what the calendar is used for.  I'm not so clear on the OU.  I know when generating utilization you have to run it from each OU.  I would think that for actual utilization it would look at the OU attached to the expenditures and that this OU field is for determining what OU to put people in for scheduled utilization.  Does it have any impact on actual utilization?