PM Schedules - Associations

When you set an association between two PM Schedules (a major service and a minor service) why would anyone set the Separate Work Order field to 1 (Separate Work Order). Wouldn't you always use 2 (Combine onto one work order). Doesn't using 1 defeat the purpose of having an association in the first place. What benefit do you get associating two service types if you then set it to create two work orders? The system doesn't even assign the same start date to the two work orders.